1. 06 Mar, 2019 40 commits
    • Aneesh Kumar K.V's avatar
      arch/powerpc/mm: Nest MMU workaround for mprotect RW upgrade · 5b323367
      Aneesh Kumar K.V authored
      NestMMU requires us to mark the pte invalid and flush the tlb when we do
      a RW upgrade of pte.  We fixed a variant of this in the fault path in
      bd5050e3 ("powerpc/mm/radix: Change pte relax sequence to handle
      nest MMU hang").
      
      Do the same for mprotect upgrades.
      
      Hugetlb is handled in the next patch.
      
      Link: http://lkml.kernel.org/r/20190116085035.29729-4-aneesh.kumar@linux.ibm.com
      
      Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Nicholas Piggin <npiggin@gmail.com>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5b323367
    • Aneesh Kumar K.V's avatar
      mm: update ptep_modify_prot_commit to take old pte value as arg · 04a86453
      Aneesh Kumar K.V authored
      Architectures like ppc64 require to do a conditional tlb flush based on
      the old and new value of pte.  Enable that by passing old pte value as
      the arg.
      
      Link: http://lkml.kernel.org/r/20190116085035.29729-3-aneesh.kumar@linux.ibm.com
      
      Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Nicholas Piggin <npiggin@gmail.com>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      04a86453
    • Aneesh Kumar K.V's avatar
      mm: update ptep_modify_prot_start/commit to take vm_area_struct as arg · 0cbe3e26
      Aneesh Kumar K.V authored
      Patch series "NestMMU pte upgrade workaround for mprotect", v5.
      
      We can upgrade pte access (R -> RW transition) via mprotect.  We need to
      make sure we follow the recommended pte update sequence as outlined in
      commit bd5050e3 ("powerpc/mm/radix: Change pte relax sequence to
      handle nest MMU hang") for such updates.  This patch series does that.
      
      This patch (of 5):
      
      Some architectures may want to call flush_tlb_range from these helpers.
      
      Link: http://lkml.kernel.org/r/20190116085035.29729-2-aneesh.kumar@linux.ibm.com
      
      Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
      Cc: Nicholas Piggin <npiggin@gmail.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      0cbe3e26
    • Wei Yang's avatar
    • Changbin Du's avatar
      mm/page_owner: move config option to mm/Kconfig.debug · 8aa49762
      Changbin Du authored
      Move the PAGE_OWNER option from submenu "Compile-time checks and
      compiler options" to dedicated submenu "Memory Debugging".
      
      Link: http://lkml.kernel.org/r/20190120024254.6270-1-changbin.du@gmail.com
      
      Signed-off-by: default avatarChangbin Du <changbin.du@gmail.com>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Arnd Bergmann <arnd@arndb.de>
      Cc: Randy Dunlap <rdunlap@infradead.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8aa49762
    • Yang Fan's avatar
      mm/mmap.c: remove some redundancy in arch_get_unmapped_area_topdown() · 43cca0b1
      Yang Fan authored
      The variable 'addr' is redundant in arch_get_unmapped_area_topdown(),
      just use parameter 'addr0' directly.  Then remove the const qualifier of
      the parameter, and change its name to 'addr'.
      
      And in according with other functions, remove the const qualifier of all
      other no-pointer parameters in function arch_get_unmapped_area_topdown().
      
      Link: http://lkml.kernel.org/r/20190127041112.25599-1-nullptr.cpp@gmail.com
      
      Signed-off-by: default avatarYang Fan <nullptr.cpp@gmail.com>
      Reviewed-by: default avatarMike Rapoport <rppt@linux.ibm.com>
      Cc: William Kucharski <william.kucharski@oracle.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      43cca0b1
    • Shakeel Butt's avatar
      mm, oom: remove 'prefer children over parent' heuristic · bbbe4802
      Shakeel Butt authored
      Since the start of the git history of Linux, the kernel after selecting
      the worst process to be oom-killed, prefer to kill its child (if the
      child does not share mm with the parent).  Later it was changed to
      prefer to kill a child who is worst.  If the parent is still the worst
      then the parent will be killed.
      
      This heuristic assumes that the children did less work than their parent
      and by killing one of them, the work lost will be less.  However this is
      very workload dependent.  If there is a workload which can benefit from
      this heuristic, can use oom_score_adj to prefer children to be killed
      before the parent.
      
      The select_bad_process() has already selected the worst process in the
      system/memcg.  There is no need to recheck the badness of its children
      and hoping to find a worse candidate.  That's a lot of unneeded racy
      work.  Also the heuristic is dangerous because it make fork bomb like
      workloads to recover much later because we constantly pick and kill
      processes which are not memory hogs.  So, let's remove this whole
      heuristic.
      
      [akpm@linux-foundation.org: coding-style fixes]
      Link: http://lkml.kernel.org/r/20190121215850.221745-2-shakeelb@google.com
      
      Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Acked-by: default avatarRoman Gushchin <guro@fb.com>
      Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      bbbe4802
    • Greg Kroah-Hartman's avatar
      mm: no need to check return value of debugfs_create functions · d9f7979c
      Greg Kroah-Hartman authored
      When calling debugfs functions, there is no need to ever check the
      return value.  The function can work or not, but the code logic should
      never do something different based on this.
      
      Link: http://lkml.kernel.org/r/20190122152151.16139-14-gregkh@linuxfoundation.org
      
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Vlastimil Babka <vbabka@suse.cz>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Laura Abbott <labbott@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d9f7979c
    • Matthew Wilcox's avatar
      mm/memory.c: prevent mapping typed pages to userspace · 0ee930e6
      Matthew Wilcox authored
      Pages which use page_type must never be mapped to userspace as it would
      destroy their page type.  Add an explicit check for this instead of
      assuming that kernel drivers always get this right.
      
      Link: http://lkml.kernel.org/r/20190129053830.3749-1-willy@infradead.org
      
      Signed-off-by: default avatarMatthew Wilcox <willy@infradead.org>
      Reviewed-by: default avatarKees Cook <keescook@chromium.org>
      Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Will Deacon <will.deacon@arm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      0ee930e6
    • Matthew Wilcox's avatar
      mm: prevent mapping slab pages to userspace · 2d432cb7
      Matthew Wilcox authored
      It's never appropriate to map a page allocated by SLAB into userspace.
      A buggy device driver might try this, or an attacker might be able to
      find a way to make it happen.
      
      Christoph said:
      
      : Let's just fail the code.  Currently this may work with SLUB.  But SLAB
      : and SLOB overlay fields with mapcount.  So you would have a corrupted page
      : struct if you mapped a slab page to user space.
      
      Link: http://lkml.kernel.org/r/20190125173827.2658-1-willy@infradead.org
      
      Signed-off-by: default avatarMatthew Wilcox <willy@infradead.org>
      Reviewed-by: default avatarKees Cook <keescook@chromium.org>
      Acked-by: default avatarPekka Enberg <penberg@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Cc: Christoph Lameter <cl@linux.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2d432cb7
    • Uladzislau Rezki (Sony)'s avatar
      mm/vmalloc.c: fix kernel BUG at mm/vmalloc.c:512! · afd07389
      Uladzislau Rezki (Sony) authored
      One of the vmalloc stress test case triggers the kernel BUG():
      
        <snip>
        [60.562151] ------------[ cut here ]------------
        [60.562154] kernel BUG at mm/vmalloc.c:512!
        [60.562206] invalid opcode: 0000 [#1] PREEMPT SMP PTI
        [60.562247] CPU: 0 PID: 430 Comm: vmalloc_test/0 Not tainted 4.20.0+ #161
        [60.562293] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
        [60.562351] RIP: 0010:alloc_vmap_area+0x36f/0x390
        <snip>
      
      it can happen due to big align request resulting in overflowing of
      calculated address, i.e.  it becomes 0 after ALIGN()'s fixup.
      
      Fix it by checking if calculated address is within vstart/vend range.
      
      Link: http://lkml.kernel.org/r/20190124115648.9433-2-urezki@gmail.com
      
      Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
      Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Joel Fernandes <joelaf@google.com>
      Cc: Matthew Wilcox <willy@infradead.org>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Thomas Garnier <thgarnie@google.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      afd07389
    • Chris Down's avatar
      mm, memcg: extract memcg maxable seq_file logic to seq_show_memcg_tunable · 677dc973
      Chris Down authored
      memcg has a significant number of files exposed to kernfs where their
      value is either exposed directly or is "max" in the case of
      PAGE_COUNTER_MAX.
      
      This patch makes this generic by providing a single function to do this
      work.  In combination with the previous patch adding
      mem_cgroup_from_seq, this makes all of the seq_show feeder functions
      significantly more simple.
      
      Link: http://lkml.kernel.org/r/20190124194100.GA31425@chrisdown.name
      
      Signed-off-by: default avatarChris Down <chris@chrisdown.name>
      Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Roman Gushchin <guro@fb.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      677dc973
    • Chris Down's avatar
      mm, memcg: create mem_cgroup_from_seq · aa9694bb
      Chris Down authored
      This is the start of a series of patches similar to my earlier
      DEFINE_MEMCG_MAX_OR_VAL work, but with less Macro Magic(tm).
      
      There are a bunch of places we go from seq_file to mem_cgroup, which
      currently requires manually getting the css, then getting the mem_cgroup
      from the css.  It's in enough places now that having mem_cgroup_from_seq
      makes sense (and also makes the next patch a bit nicer).
      
      Link: http://lkml.kernel.org/r/20190124194050.GA31341@chrisdown.name
      
      Signed-off-by: default avatarChris Down <chris@chrisdown.name>
      Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Roman Gushchin <guro@fb.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      aa9694bb
    • Johannes Weiner's avatar
      kernel: cgroup: add poll file operation · dc50537b
      Johannes Weiner authored
      Cgroup has a standardized poll/notification mechanism for waking all
      pollers on all fds when a filesystem node changes.  To allow polling for
      custom events, add a .poll callback that can override the default.
      
      This is in preparation for pollable cgroup pressure files which have
      per-fd trigger configurations.
      
      Link: http://lkml.kernel.org/r/20190124211518.244221-3-surenb@google.com
      
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarSuren Baghdasaryan <surenb@google.com>
      Cc: Dennis Zhou <dennis@kernel.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Li Zefan <lizefan@huawei.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Tejun Heo <tj@kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      dc50537b
    • Johannes Weiner's avatar
      fs: kernfs: add poll file operation · 147e1a97
      Johannes Weiner authored
      Patch series "psi: pressure stall monitors", v3.
      
      Android is adopting psi to detect and remedy memory pressure that
      results in stuttering and decreased responsiveness on mobile devices.
      
      Psi gives us the stall information, but because we're dealing with
      latencies in the millisecond range, periodically reading the pressure
      files to detect stalls in a timely fashion is not feasible.  Psi also
      doesn't aggregate its averages at a high enough frequency right now.
      
      This patch series extends the psi interface such that users can
      configure sensitive latency thresholds and use poll() and friends to be
      notified when these are breached.
      
      As high-frequency aggregation is costly, it implements an aggregation
      method that is optimized for fast, short-interval averaging, and makes
      the aggregation frequency adaptive, such that high-frequency updates
      only happen while monitored stall events are actively occurring.
      
      With these patches applied, Android can monitor for, and ward off,
      mounting memory shortages before they cause problems for the user.  For
      example, using memory stall monitors in userspace low memory killer
      daemon (lmkd) we can detect mounting pressure and kill less important
      processes before device becomes visibly sluggish.
      
      In our memory stress testing psi memory monitors produce roughly 10x
      less false positives compared to vmpressure signals.  Having ability to
      specify multiple triggers for the same psi metric allows other parts of
      Android framework to monitor memory state of the device and act
      accordingly.
      
      The new interface is straightforward.  The user opens one of the
      pressure files for writing and writes a trigger description into the
      file descriptor that defines the stall state - some or full, and the
      maximum stall time over a given window of time.  E.g.:
      
              /* Signal when stall time exceeds 100ms of a 1s window */
              char trigger[] = "full 100000 1000000";
              fd = open("/proc/pressure/memory");
              write(fd, trigger, sizeof(trigger));
              while (poll() >= 0) {
                      ...
              }
              close(fd);
      
      When the monitored stall state is entered, psi adapts its aggregation
      frequency according to what the configured time window requires in order
      to emit event signals in a timely fashion.  Once the stalling subsides,
      aggregation reverts back to normal.
      
      The trigger is associated with the open file descriptor.  To stop
      monitoring, the user only needs to close the file descriptor and the
      trigger is discarded.
      
      Patches 1-4 prepare the psi code for polling support.  Patch 5
      implements the adaptive polling logic, the pressure growth detection
      optimized for short intervals, and hooks up write() and poll() on the
      pressure files.
      
      The patches were developed in collaboration with Johannes Weiner.
      
      This patch (of 5):
      
      Kernfs has a standardized poll/notification mechanism for waking all
      pollers on all fds when a filesystem node changes.  To allow polling for
      custom events, add a .poll callback that can override the default.
      
      This is in preparation for pollable cgroup pressure files which have
      per-fd trigger configurations.
      
      Link: http://lkml.kernel.org/r/20190124211518.244221-2-surenb@google.com
      
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarSuren Baghdasaryan <surenb@google.com>
      Cc: Dennis Zhou <dennis@kernel.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Li Zefan <lizefan@huawei.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Tejun Heo <tj@kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      147e1a97
    • Mel Gorman's avatar
      mm, compaction: capture a page under direct compaction · 5e1f0f09
      Mel Gorman authored
      Compaction is inherently race-prone as a suitable page freed during
      compaction can be allocated by any parallel task.  This patch uses a
      capture_control structure to isolate a page immediately when it is freed
      by a direct compactor in the slow path of the page allocator.  The
      intent is to avoid redundant scanning.
      
                                           5.0.0-rc1              5.0.0-rc1
                                     selective-v3r17          capture-v3r19
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      2582.11 (   0.00%)     2563.68 (   0.71%)
      Amean     fault-both-5      4500.26 (   0.00%)     4233.52 (   5.93%)
      Amean     fault-both-7      5819.53 (   0.00%)     6333.65 (  -8.83%)
      Amean     fault-both-12     9321.18 (   0.00%)     9759.38 (  -4.70%)
      Amean     fault-both-18     9782.76 (   0.00%)    10338.76 (  -5.68%)
      Amean     fault-both-24    15272.81 (   0.00%)    13379.55 *  12.40%*
      Amean     fault-both-30    15121.34 (   0.00%)    16158.25 (  -6.86%)
      Amean     fault-both-32    18466.67 (   0.00%)    18971.21 (  -2.73%)
      
      Latency is only moderately affected but the devil is in the details.  A
      closer examination indicates that base page fault latency is reduced but
      latency of huge pages is increased as it takes creater care to succeed.
      Part of the "problem" is that allocation success rates are close to 100%
      even when under pressure and compaction gets harder
      
                                      5.0.0-rc1              5.0.0-rc1
                                selective-v3r17          capture-v3r19
      Percentage huge-3        96.70 (   0.00%)       98.23 (   1.58%)
      Percentage huge-5        96.99 (   0.00%)       95.30 (  -1.75%)
      Percentage huge-7        94.19 (   0.00%)       97.24 (   3.24%)
      Percentage huge-12       94.95 (   0.00%)       97.35 (   2.53%)
      Percentage huge-18       96.74 (   0.00%)       97.30 (   0.58%)
      Percentage huge-24       97.07 (   0.00%)       97.55 (   0.50%)
      Percentage huge-30       95.69 (   0.00%)       98.50 (   2.95%)
      Percentage huge-32       96.70 (   0.00%)       99.27 (   2.65%)
      
      And scan rates are reduced as expected by 6% for the migration scanner
      and 29% for the free scanner indicating that there is less redundant
      work.
      
      Compaction migrate scanned    20815362    19573286
      Compaction free scanned       16352612    11510663
      
      [mgorman@techsingularity.net: remove redundant check]
        Link: http://lkml.kernel.org/r/20190201143853.GH9565@techsingularity.net
      Link: http://lkml.kernel.org/r/20190118175136.31341-23-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5e1f0f09
    • Mel Gorman's avatar
      mm, compaction: be selective about what pageblocks to clear skip hints · e332f741
      Mel Gorman authored
      Pageblock hints are cleared when compaction restarts or kswapd makes
      enough progress that it can sleep but it's over-eager in that the bit is
      cleared for migration sources with no LRU pages and migration targets
      with no free pages.  As pageblock skip hint flushes are relatively rare
      and out-of-band with respect to kswapd, this patch makes a few more
      expensive checks to see if it's appropriate to even clear the bit.
      Every pageblock that is not cleared will avoid 512 pages being scanned
      unnecessarily on x86-64.
      
      The impact is variable with different workloads showing small
      differences in latency, success rates and scan rates.  This is expected
      as clearing the hints is not that common but doing a small amount of
      work out-of-band to avoid a large amount of work in-band later is
      generally a good thing.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-22-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Signed-off-by: default avatarQian Cai <cai@lca.pw>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      [cai@lca.pw: no stuck in __reset_isolation_pfn()]
        Link: http://lkml.kernel.org/r/20190206034732.75687-1-cai@lca.pw
      
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      e332f741
    • Mel Gorman's avatar
      mm, compaction: sample pageblocks for free pages · 4fca9730
      Mel Gorman authored
      Once fast searching finishes, there is a possibility that the linear
      scanner is scanning full blocks found by the fast scanner earlier.  This
      patch uses an adaptive stride to sample pageblocks for free pages.  The
      more consecutive full pageblocks encountered, the larger the stride
      until a pageblock with free pages is found.  The scanners might meet
      slightly sooner but it is an acceptable risk given that the search of
      the free lists may still encounter the pages and adjust the cached PFN
      of the free scanner accordingly.
      
                                           5.0.0-rc1              5.0.0-rc1
                                    roundrobin-v3r17       samplefree-v3r17
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      2752.37 (   0.00%)     2729.95 (   0.81%)
      Amean     fault-both-5      4341.69 (   0.00%)     4397.80 (  -1.29%)
      Amean     fault-both-7      6308.75 (   0.00%)     6097.61 (   3.35%)
      Amean     fault-both-12    10241.81 (   0.00%)     9407.15 (   8.15%)
      Amean     fault-both-18    13736.09 (   0.00%)    10857.63 *  20.96%*
      Amean     fault-both-24    16853.95 (   0.00%)    13323.24 *  20.95%*
      Amean     fault-both-30    15862.61 (   0.00%)    17345.44 (  -9.35%)
      Amean     fault-both-32    18450.85 (   0.00%)    16892.00 (   8.45%)
      
      The latency is mildly improved offseting some overhead from earlier
      patches that are prerequisites for the rest of the series.  However, a
      major impact is on the free scan rate with an 82% reduction.
      
                                      5.0.0-rc1      5.0.0-rc1
                               roundrobin-v3r17 samplefree-v3r17
      Compaction migrate scanned    21607271            20116887
      Compaction free scanned       95336406            16668703
      
      It's also the first time in the series where the number of pages scanned
      by the migration scanner is greater than the free scanner due to the
      increased search efficiency.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-21-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4fca9730
    • Mel Gorman's avatar
      mm, compaction: round-robin the order while searching the free lists for a target · dbe2d4e4
      Mel Gorman authored
      As compaction proceeds and creates high-order blocks, the free list
      search gets less efficient as the larger blocks are used as compaction
      targets.  Eventually, the larger blocks will be behind the migration
      scanner for partially migrated pageblocks and the search fails.  This
      patch round-robins what orders are searched so that larger blocks can be
      ignored and find smaller blocks that can be used as migration targets.
      
      The overall impact was small on 1-socket but it avoids corner cases
      where the migration/free scanners meet prematurely or situations where
      many of the pageblocks encountered by the free scanner are almost full
      instead of being properly packed.  Previous testing had indicated that
      without this patch there were occasional large spikes in the free
      scanner without this patch.
      
      [dan.carpenter@oracle.com: fix static checker warning]
      Link: http://lkml.kernel.org/r/20190118175136.31341-20-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      dbe2d4e4
    • Mel Gorman's avatar
      mm, compaction: reduce premature advancement of the migration target scanner · d097a6f6
      Mel Gorman authored
      The fast isolation of free pages allows the cached PFN of the free
      scanner to advance faster than necessary depending on the contents of
      the free list.  The key is that fast_isolate_freepages() can update
      zone->compact_cached_free_pfn via isolate_freepages_block().  When the
      fast search fails, the linear scan can start from a point that has
      skipped valid migration targets, particularly pageblocks with just
      low-order free pages.  This can cause the migration source/target
      scanners to meet prematurely causing a reset.
      
      This patch starts by avoiding an update of the pageblock skip
      information and cached PFN from isolate_freepages_block() and puts the
      responsibility of updating that information in the callers.  The fast
      scanner will update the cached PFN if and only if it finds a block that
      is higher than the existing cached PFN and sets the skip if the
      pageblock is full or nearly full.  The linear scanner will update
      skipped information and the cached PFN only when a block is completely
      scanned.  The total impact is that the free scanner advances more slowly
      as it is primarily driven by the linear scanner instead of the fast
      search.
      
                                           5.0.0-rc1              5.0.0-rc1
                                     noresched-v3r17         slowfree-v3r17
      Amean     fault-both-3      2965.68 (   0.00%)     3036.75 (  -2.40%)
      Amean     fault-both-5      3995.90 (   0.00%)     4522.24 * -13.17%*
      Amean     fault-both-7      5842.12 (   0.00%)     6365.35 (  -8.96%)
      Amean     fault-both-12     9550.87 (   0.00%)    10340.93 (  -8.27%)
      Amean     fault-both-18    13304.72 (   0.00%)    14732.46 ( -10.73%)
      Amean     fault-both-24    14618.59 (   0.00%)    16288.96 ( -11.43%)
      Amean     fault-both-30    16650.96 (   0.00%)    16346.21 (   1.83%)
      Amean     fault-both-32    17145.15 (   0.00%)    19317.49 ( -12.67%)
      
      The impact to latency is higher than the last version but it appears to
      be due to a slight increase in the free scan rates which is a potential
      side-effect of the patch.  However, this is necessary for later patches
      that are more careful about how pageblocks are treated as earlier
      iterations of those patches hit corner cases where the restarts were
      punishing and very visible.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-19-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d097a6f6
    • Mel Gorman's avatar
      mm, compaction: do not consider a need to reschedule as contention · cf66f070
      Mel Gorman authored
      Scanning on large machines can take a considerable length of time and
      eventually need to be rescheduled.  This is treated as an abort event
      but that's not appropriate as the attempt is likely to be retried after
      making numerous checks and taking another cycle through the page
      allocator.  This patch will check the need to reschedule if necessary
      but continue the scanning.
      
      The main benefit is reduced scanning when compaction is taking a long
      time or the machine is over-saturated.  It also avoids an unnecessary
      exit of compaction that ends up being retried by the page allocator in
      the outer loop.
      
                                           5.0.0-rc1              5.0.0-rc1
                                    synccached-v3r16        noresched-v3r17
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      2958.27 (   0.00%)     2965.68 (  -0.25%)
      Amean     fault-both-5      4091.90 (   0.00%)     3995.90 (   2.35%)
      Amean     fault-both-7      5803.05 (   0.00%)     5842.12 (  -0.67%)
      Amean     fault-both-12     9481.06 (   0.00%)     9550.87 (  -0.74%)
      Amean     fault-both-18    14141.51 (   0.00%)    13304.72 (   5.92%)
      Amean     fault-both-24    16438.00 (   0.00%)    14618.59 (  11.07%)
      Amean     fault-both-30    17531.72 (   0.00%)    16650.96 (   5.02%)
      Amean     fault-both-32    17101.96 (   0.00%)    17145.15 (  -0.25%)
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-18-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      cf66f070
    • Mel Gorman's avatar
      mm, compaction: rework compact_should_abort as compact_check_resched · cb810ad2
      Mel Gorman authored
      With incremental changes, compact_should_abort no longer makes any
      documented sense.  Rename to compact_check_resched and update the
      associated comments.  There is no benefit other than reducing redundant
      code and making the intent slightly clearer.  It could potentially be
      merged with earlier patches but it just makes the review slightly
      harder.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-17-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      cb810ad2
    • Mel Gorman's avatar
      mm, compaction: keep cached migration PFNs synced for unusable pageblocks · 8854c55f
      Mel Gorman authored
      Migrate has separate cached PFNs for ASYNC and SYNC* migration on the
      basis that some migrations will fail in ASYNC mode.  However, if the
      cached PFNs match at the start of scanning and pageblocks are skipped
      due to having no isolation candidates, then the sync state does not
      matter.  This patch keeps matching cached PFNs in sync until a pageblock
      with isolation candidates is found.
      
      The actual benefit is marginal given that the sync scanner following the
      async scanner will often skip a number of pageblocks but it's useless
      work.  Any benefit depends heavily on whether the scanners restarted
      recently.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-16-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8854c55f
    • Mel Gorman's avatar
      mm, compaction: check early for huge pages encountered by the migration scanner · 9bebefd5
      Mel Gorman authored
      When scanning for sources or targets, PageCompound is checked for huge
      pages as they can be skipped quickly but it happens relatively late
      after a lot of setup and checking.  This patch short-cuts the check to
      make it earlier.  It might still change when the lock is acquired but
      this has less overhead overall.  The free scanner advances but the
      migration scanner does not.  Typically the free scanner encounters more
      movable blocks that change state over the lifetime of the system and
      also tends to scan more aggressively as it's actively filling its
      portion of the physical address space with data.  This could change in
      the future but for the moment, this worked better in practice and
      incurred fewer scan restarts.
      
      The impact on latency and allocation success rates is marginal but the
      free scan rates are reduced by 15% and system CPU usage is reduced by
      3.3%.  The 2-socket results are not materially different.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-15-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      9bebefd5
    • Mel Gorman's avatar
      mm, compaction: finish pageblock scanning on contention · cb2dcaf0
      Mel Gorman authored
      Async migration aborts on spinlock contention but contention can be high
      when there are multiple compaction attempts and kswapd is active.  The
      consequence is that the migration scanners move forward uselessly while
      still contending on locks for longer while leaving suitable migration
      sources behind.
      
      This patch will acquire the lock but track when contention occurs.  When
      it does, the current pageblock will finish as compaction may succeed for
      that block and then abort.  This will have a variable impact on latency
      as in some cases useless scanning is avoided (reduces latency) but a
      lock will be contended (increase latency) or a single contended
      pageblock is scanned that would otherwise have been skipped (increase
      latency).
      
                                           5.0.0-rc1              5.0.0-rc1
                                      norescan-v3r16    finishcontend-v3r16
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      3002.07 (   0.00%)     3153.17 (  -5.03%)
      Amean     fault-both-5      4684.47 (   0.00%)     4280.52 (   8.62%)
      Amean     fault-both-7      6815.54 (   0.00%)     5811.50 *  14.73%*
      Amean     fault-both-12    10864.02 (   0.00%)     9276.85 (  14.61%)
      Amean     fault-both-18    12247.52 (   0.00%)    11032.67 (   9.92%)
      Amean     fault-both-24    15683.99 (   0.00%)    14285.70 (   8.92%)
      Amean     fault-both-30    18620.02 (   0.00%)    16293.76 *  12.49%*
      Amean     fault-both-32    19250.28 (   0.00%)    16721.02 *  13.14%*
      
                                      5.0.0-rc1              5.0.0-rc1
                                 norescan-v3r16    finishcontend-v3r16
      Percentage huge-1         0.00 (   0.00%)        0.00 (   0.00%)
      Percentage huge-3        95.00 (   0.00%)       96.82 (   1.92%)
      Percentage huge-5        94.22 (   0.00%)       95.40 (   1.26%)
      Percentage huge-7        92.35 (   0.00%)       95.92 (   3.86%)
      Percentage huge-12       91.90 (   0.00%)       96.73 (   5.25%)
      Percentage huge-18       89.58 (   0.00%)       96.77 (   8.03%)
      Percentage huge-24       90.03 (   0.00%)       96.05 (   6.69%)
      Percentage huge-30       89.14 (   0.00%)       96.81 (   8.60%)
      Percentage huge-32       90.58 (   0.00%)       97.41 (   7.54%)
      
      There is a variable impact that is mostly good on latency while allocation
      success rates are slightly higher.  System CPU usage is reduced by about
      10% but scan rate impact is mixed
      
      Compaction migrate scanned    27997659.00    20148867
      Compaction free scanned      120782791.00   118324914
      
      Migration scan rates are reduced 28% which is expected as a pageblock is
      used by the async scanner instead of skipped.  The impact on the free
      scanner is known to be variable.  Overall the primary justification for
      this patch is that completing scanning of a pageblock is very important
      for later patches.
      
      [yuehaibing@huawei.com: fix unused variable warning]
      Link: http://lkml.kernel.org/r/20190118175136.31341-14-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      cb2dcaf0
    • Mel Gorman's avatar
      mm, compaction: avoid rescanning the same pageblock multiple times · 804d3121
      Mel Gorman authored
      Pageblocks are marked for skip when no pages are isolated after a scan.
      However, it's possible to hit corner cases where the migration scanner
      gets stuck near the boundary between the source and target scanner.  Due
      to pages being migrated in blocks of COMPACT_CLUSTER_MAX, pages that are
      migrated can be reallocated before the pageblock is complete.  The
      pageblock is not necessarily skipped so it can be rescanned multiple
      times.  Similarly, a pageblock with some dirty/writeback pages may fail
      to migrate and be rescanned until writeback completes which is wasteful.
      
      This patch tracks if a pageblock is being rescanned.  If so, then the
      entire pageblock will be migrated as one operation.  This narrows the
      race window during which pages can be reallocated during migration.
      Secondly, if there are pages that cannot be isolated then the pageblock
      will still be fully scanned and marked for skipping.  On the second
      rescan, the pageblock skip is set and the migration scanner makes
      progress.
      
                                           5.0.0-rc1              5.0.0-rc1
                                      findfree-v3r16         norescan-v3r16
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      3200.68 (   0.00%)     3002.07 (   6.21%)
      Amean     fault-both-5      4847.75 (   0.00%)     4684.47 (   3.37%)
      Amean     fault-both-7      6658.92 (   0.00%)     6815.54 (  -2.35%)
      Amean     fault-both-12    11077.62 (   0.00%)    10864.02 (   1.93%)
      Amean     fault-both-18    12403.97 (   0.00%)    12247.52 (   1.26%)
      Amean     fault-both-24    15607.10 (   0.00%)    15683.99 (  -0.49%)
      Amean     fault-both-30    18752.27 (   0.00%)    18620.02 (   0.71%)
      Amean     fault-both-32    21207.54 (   0.00%)    19250.28 *   9.23%*
      
                                      5.0.0-rc1              5.0.0-rc1
                                 findfree-v3r16         norescan-v3r16
      Percentage huge-3        96.86 (   0.00%)       95.00 (  -1.91%)
      Percentage huge-5        93.72 (   0.00%)       94.22 (   0.53%)
      Percentage huge-7        94.31 (   0.00%)       92.35 (  -2.08%)
      Percentage huge-12       92.66 (   0.00%)       91.90 (  -0.82%)
      Percentage huge-18       91.51 (   0.00%)       89.58 (  -2.11%)
      Percentage huge-24       90.50 (   0.00%)       90.03 (  -0.52%)
      Percentage huge-30       91.57 (   0.00%)       89.14 (  -2.65%)
      Percentage huge-32       91.00 (   0.00%)       90.58 (  -0.46%)
      
      Negligible difference but this was likely a case when the specific
      corner case was not hit.  A previous run of the same patch based on an
      earlier iteration of the series showed large differences where migration
      rates could be halved when the corner case was hit.
      
      The specific corner case where migration scan rates go through the roof
      was due to a dirty/writeback pageblock located at the boundary of the
      migration/free scanner did not happen in this case.  When it does
      happen, the scan rates multipled by massive margins.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-13-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      804d3121
    • Mel Gorman's avatar
      mm, compaction: use free lists to quickly locate a migration target · 5a811889
      Mel Gorman authored
      Similar to the migration scanner, this patch uses the free lists to
      quickly locate a migration target.  The search is different in that
      lower orders will be searched for a suitable high PFN if necessary but
      the search is still bound.  This is justified on the grounds that the
      free scanner typically scans linearly much more than the migration
      scanner.
      
      If a free page is found, it is isolated and compaction continues if
      enough pages were isolated.  For SYNC* scanning, the full pageblock is
      scanned for any remaining free pages so that is can be marked for
      skipping in the near future.
      
      1-socket thpfioscale
                                           5.0.0-rc1              5.0.0-rc1
                                       isolmig-v3r15         findfree-v3r16
      Amean     fault-both-3      3024.41 (   0.00%)     3200.68 (  -5.83%)
      Amean     fault-both-5      4749.30 (   0.00%)     4847.75 (  -2.07%)
      Amean     fault-both-7      6454.95 (   0.00%)     6658.92 (  -3.16%)
      Amean     fault-both-12    10324.83 (   0.00%)    11077.62 (  -7.29%)
      Amean     fault-both-18    12896.82 (   0.00%)    12403.97 (   3.82%)
      Amean     fault-both-24    13470.60 (   0.00%)    15607.10 * -15.86%*
      Amean     fault-both-30    17143.99 (   0.00%)    18752.27 (  -9.38%)
      Amean     fault-both-32    17743.91 (   0.00%)    21207.54 * -19.52%*
      
      The impact on latency is variable but the search is optimistic and
      sensitive to the exact system state.  Success rates are similar but the
      major impact is to the rate of scanning
      
                                      5.0.0-rc1      5.0.0-rc1
                                  isolmig-v3r15 findfree-v3r16
      Compaction migrate scanned    25646769          29507205
      Compaction free scanned      201558184         100359571
      
      The free scan rates are reduced by 50%.  The 2-socket reductions for the
      free scanner are more dramatic which is a likely reflection that the
      machine has more memory.
      
      [dan.carpenter@oracle.com: fix static checker warning]
      [vbabka@suse.cz: correct number of pages scanned for lower orders]
      Link: http://lkml.kernel.org/r/20190118175136.31341-12-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5a811889
    • Mel Gorman's avatar
      mm, compaction: keep migration source private to a single compaction instance · e380bebe
      Mel Gorman authored
      Due to either a fast search of the free list or a linear scan, it is
      possible for multiple compaction instances to pick the same pageblock
      for migration.  This is lucky for one scanner and increased scanning for
      all the others.  It also allows a race between requests on which first
      allocates the resulting free block.
      
      This patch tests and updates the pageblock skip for the migration
      scanner carefully.  When isolating a block, it will check and skip if
      the block is already in use.  Once the zone lock is acquired, it will be
      rechecked so that only one scanner can set the pageblock skip for
      exclusive use.  Any scanner contending will continue with a linear scan.
      The skip bit is still set if no pages can be isolated in a range.  While
      this may result in redundant scanning, it avoids unnecessarily acquiring
      the zone lock when there are no suitable migration sources.
      
      1-socket thpscale
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      3390.40 (   0.00%)     3024.41 (  10.80%)
      Amean     fault-both-5      5082.28 (   0.00%)     4749.30 (   6.55%)
      Amean     fault-both-7      7012.51 (   0.00%)     6454.95 (   7.95%)
      Amean     fault-both-12    11346.63 (   0.00%)    10324.83 (   9.01%)
      Amean     fault-both-18    15324.19 (   0.00%)    12896.82 *  15.84%*
      Amean     fault-both-24    16088.50 (   0.00%)    13470.60 *  16.27%*
      Amean     fault-both-30    18723.42 (   0.00%)    17143.99 (   8.44%)
      Amean     fault-both-32    18612.01 (   0.00%)    17743.91 (   4.66%)
      
                                      5.0.0-rc1              5.0.0-rc1
                                  findmig-v3r15          isolmig-v3r15
      Percentage huge-3        89.83 (   0.00%)       92.96 (   3.48%)
      Percentage huge-5        91.96 (   0.00%)       93.26 (   1.41%)
      Percentage huge-7        92.85 (   0.00%)       93.63 (   0.84%)
      Percentage huge-12       92.74 (   0.00%)       92.80 (   0.07%)
      Percentage huge-18       91.71 (   0.00%)       91.62 (  -0.10%)
      Percentage huge-24       92.13 (   0.00%)       91.50 (  -0.69%)
      Percentage huge-30       93.79 (   0.00%)       92.73 (  -1.13%)
      Percentage huge-32       91.27 (   0.00%)       91.94 (   0.74%)
      
      This shows a reasonable reduction in latency as multiple compaction
      scanners do not operate on the same blocks with a similar allocation
      success rate.
      
      Compaction migrate scanned    41093126    25646769
      
      Migration scan rates are reduced by 38%.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-11-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      e380bebe
    • Mel Gorman's avatar
      mm, compaction: use free lists to quickly locate a migration source · 70b44595
      Mel Gorman authored
      The migration scanner is a linear scan of a zone with a potentiall large
      search space.  Furthermore, many pageblocks are unusable such as those
      filled with reserved pages or partially filled with pages that cannot
      migrate.  These still get scanned in the common case of allocating a THP
      and the cost accumulates.
      
      The patch uses a partial search of the free lists to locate a migration
      source candidate that is marked as MOVABLE when allocating a THP.  It
      prefers picking a block with a larger number of free pages already on
      the basis that there are fewer pages to migrate to free the entire
      block.  The lowest PFN found during searches is tracked as the basis of
      the start for the linear search after the first search of the free list
      fails.  After the search, the free list is shuffled so that the next
      search will not encounter the same page.  If the search fails then the
      subsequent searches will be shorter and the linear scanner is used.
      
      If this search fails, or if the request is for a small or
      unmovable/reclaimable allocation then the linear scanner is still used.
      It is somewhat pointless to use the list search in those cases.  Small
      free pages must be used for the search and there is no guarantee that
      movable pages are located within that block that are contiguous.
      
                                           5.0.0-rc1              5.0.0-rc1
                                       noboost-v3r10          findmig-v3r15
      Amean     fault-both-3      3771.41 (   0.00%)     3390.40 (  10.10%)
      Amean     fault-both-5      5409.05 (   0.00%)     5082.28 (   6.04%)
      Amean     fault-both-7      7040.74 (   0.00%)     7012.51 (   0.40%)
      Amean     fault-both-12    11887.35 (   0.00%)    11346.63 (   4.55%)
      Amean     fault-both-18    16718.19 (   0.00%)    15324.19 (   8.34%)
      Amean     fault-both-24    21157.19 (   0.00%)    16088.50 *  23.96%*
      Amean     fault-both-30    21175.92 (   0.00%)    18723.42 *  11.58%*
      Amean     fault-both-32    21339.03 (   0.00%)    18612.01 *  12.78%*
      
                                      5.0.0-rc1              5.0.0-rc1
                                  noboost-v3r10          findmig-v3r15
      Percentage huge-3        86.50 (   0.00%)       89.83 (   3.85%)
      Percentage huge-5        92.52 (   0.00%)       91.96 (  -0.61%)
      Percentage huge-7        92.44 (   0.00%)       92.85 (   0.44%)
      Percentage huge-12       92.98 (   0.00%)       92.74 (  -0.25%)
      Percentage huge-18       91.70 (   0.00%)       91.71 (   0.02%)
      Percentage huge-24       91.59 (   0.00%)       92.13 (   0.60%)
      Percentage huge-30       90.14 (   0.00%)       93.79 (   4.04%)
      Percentage huge-32       90.03 (   0.00%)       91.27 (   1.37%)
      
      This shows an improvement in allocation latencies with similar
      allocation success rates.  While not presented, there was a 31%
      reduction in migration scanning and a 8% reduction on system CPU usage.
      A 2-socket machine showed similar benefits.
      
      [mgorman@techsingularity.net: several fixes]
        Link: http://lkml.kernel.org/r/20190204120111.GL9565@techsingularity.net
      [vbabka@suse.cz: migrate block that was found-fast, some optimisations]
      Link: http://lkml.kernel.org/r/20190118175136.31341-10-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <Vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      70b44595
    • Mel Gorman's avatar
      mm, compaction: ignore the fragmentation avoidance boost for isolation and compaction · fd1444b2
      Mel Gorman authored
      When pageblocks get fragmented, watermarks are artifically boosted to
      reclaim pages to avoid further fragmentation events.  However,
      compaction is often either fragmentation-neutral or moving movable pages
      away from unmovable/reclaimable pages.  As the true watermarks are
      preserved, allow compaction to ignore the boost factor.
      
      The expected impact is very slight as the main benefit is that
      compaction is slightly more likely to succeed when the system has been
      fragmented very recently.  On both 1-socket and 2-socket machines for
      THP-intensive allocation during fragmentation the success rate was
      increased by less than 1% which is marginal.  However, detailed tracing
      indicated that failure of migration due to a premature ENOMEM triggered
      by watermark checks were eliminated.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-9-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      fd1444b2
    • Mel Gorman's avatar
      mm, compaction: always finish scanning of a full pageblock · efe771c7
      Mel Gorman authored
      When compaction is finishing, it uses a flag to ensure the pageblock is
      complete but it makes sense to always complete migration of a pageblock.
      Minimally, skip information is based on a pageblock and partially
      scanned pageblocks may incur more scanning in the future.  The pageblock
      skip handling also becomes more strict later in the series and the hint
      is more useful if a complete pageblock was always scanned.
      
      The potentially impacts latency as more scanning is done but it's not a
      consistent win or loss as the scanning is not always a high percentage
      of the pageblock and sometimes it is offset by future reductions in
      scanning.  Hence, the results are not presented this time due to a
      misleading mix of gains/losses without any clear pattern.  However, full
      scanning of the pageblock is important for later patches.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-8-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      efe771c7
    • Mel Gorman's avatar
      mm, migrate: immediately fail migration of a page with no migration handler · 806031bb
      Mel Gorman authored
      Pages with no migration handler use a fallback handler which sometimes
      works and sometimes persistently retries.  A historical example was
      blockdev pages but there are others such as odd refcounting when
      page->private is used.  These are retried multiple times which is
      wasteful during compaction so this patch will fail migration faster
      unless the caller specifies MIGRATE_SYNC.
      
      This is not expected to help THP allocation success rates but it did
      reduce latencies very slightly in some cases.
      
      1-socket thpfioscale
                                              4.20.0                 4.20.0
                                    noreserved-v2r15         failfast-v2r15
      Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
      Amean     fault-both-3      3839.67 (   0.00%)     3833.72 (   0.15%)
      Amean     fault-both-5      5177.47 (   0.00%)     4967.15 (   4.06%)
      Amean     fault-both-7      7245.03 (   0.00%)     7139.19 (   1.46%)
      Amean     fault-both-12    11534.89 (   0.00%)    11326.30 (   1.81%)
      Amean     fault-both-18    16241.10 (   0.00%)    16270.70 (  -0.18%)
      Amean     fault-both-24    19075.91 (   0.00%)    19839.65 (  -4.00%)
      Amean     fault-both-30    22712.11 (   0.00%)    21707.05 (   4.43%)
      Amean     fault-both-32    21692.92 (   0.00%)    21968.16 (  -1.27%)
      
      The 2-socket results are not materially different.  Scan rates are
      similar as expected.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-7-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      806031bb
    • Mel Gorman's avatar
      mm, compaction: rename map_pages to split_map_pages · 4469ab98
      Mel Gorman authored
      It's non-obvious that high-order free pages are split into order-0 pages
      from the function name.  Fix it.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-6-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4469ab98
    • Mel Gorman's avatar
      mm, compaction: remove unnecessary zone parameter in some instances · 40cacbcb
      Mel Gorman authored
      A zone parameter is passed into a number of top-level compaction
      functions despite the fact that it's already in compact_control.  This
      is harmless but it did need an audit to check if zone actually ever
      changes meaningfully.  This patches removes the parameter in a number of
      top-level functions.  The change could be much deeper but this was
      enough to briefly clarify the flow.
      
      No functional change.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-5-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      40cacbcb
    • Mel Gorman's avatar
      mm, compaction: remove last_migrated_pfn from compact_control · 566e54e1
      Mel Gorman authored
      The last_migrated_pfn field is a bit dubious as to whether it really
      helps but either way, the information from it can be inferred without
      increasing the size of compact_control so remove the field.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-4-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      566e54e1
    • Mel Gorman's avatar
      mm, compaction: rearrange compact_control · c5943b9c
      Mel Gorman authored
      compact_control spans two cache lines with write-intensive lines on
      both.  Rearrange so the most write-intensive fields are in the same
      cache line.  This has a negligible impact on the overall performance of
      compaction and is more a tidying exercise than anything.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-3-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c5943b9c
    • Mel Gorman's avatar
      mm, compaction: shrink compact_control · c5fbd937
      Mel Gorman authored
      Patch series "Increase success rates and reduce latency of compaction", v3.
      
      This series reduces scan rates and success rates of compaction,
      primarily by using the free lists to shorten scans, better controlling
      of skip information and whether multiple scanners can target the same
      block and capturing pageblocks before being stolen by parallel requests.
      The series is based on mmotm from January 9th, 2019 with the previous
      compaction series reverted.
      
      I'm mostly using thpscale to measure the impact of the series.  The
      benchmark creates a large file, maps it, faults it, punches holes in the
      mapping so that the virtual address space is fragmented and then tries
      to allocate THP.  It re-executes for different numbers of threads.  From
      a fragmentation perspective, the workload is relatively benign but it
      does stress compaction.
      
      The overall impact on latencies for a 1-socket machine is
      
      				      baseline		      patches
      Amean     fault-both-3      3832.09 (   0.00%)     2748.56 *  28.28%*
      Amean     fault-both-5      4933.06 (   0.00%)     4255.52 (  13.73%)
      Amean     fault-both-7      7017.75 (   0.00%)     6586.93 (   6.14%)
      Amean     fault-both-12    11610.51 (   0.00%)     9162.34 *  21.09%*
      Amean     fault-both-18    17055.85 (   0.00%)    11530.06 *  32.40%*
      Amean     fault-both-24    19306.27 (   0.00%)    17956.13 (   6.99%)
      Amean     fault-both-30    22516.49 (   0.00%)    15686.47 *  30.33%*
      Amean     fault-both-32    23442.93 (   0.00%)    16564.83 *  29.34%*
      
      The allocation success rates are much improved
      
      			 	 baseline		 patches
      Percentage huge-3        85.99 (   0.00%)       97.96 (  13.92%)
      Percentage huge-5        88.27 (   0.00%)       96.87 (   9.74%)
      Percentage huge-7        85.87 (   0.00%)       94.53 (  10.09%)
      Percentage huge-12       82.38 (   0.00%)       98.44 (  19.49%)
      Percentage huge-18       83.29 (   0.00%)       99.14 (  19.04%)
      Percentage huge-24       81.41 (   0.00%)       97.35 (  19.57%)
      Percentage huge-30       80.98 (   0.00%)       98.05 (  21.08%)
      Percentage huge-32       80.53 (   0.00%)       97.06 (  20.53%)
      
      That's a nearly perfect allocation success rate.
      
      The biggest impact is on the scan rates
      
      Compaction migrate scanned    55893379    19341254
      Compaction free scanned      474739990    11903963
      
      The number of pages scanned for migration was reduced by 65% and the
      free scanner was reduced by 97.5%.  So much less work in exchange for
      lower latency and better success rates.
      
      The series was also evaluated using a workload that heavily fragments
      memory but the benefits there are also significant, albeit not
      presented.
      
      It was commented that we should be rethinking scanning entirely and to a
      large extent I agree.  However, to achieve that you need a lot of this
      series in place first so it's best to make the linear scanners as best
      as possible before ripping them out.
      
      This patch (of 22):
      
      The isolate and migrate scanners should never isolate more than a
      pageblock of pages so unsigned int is sufficient saving 8 bytes on a
      64-bit build.
      
      Link: http://lkml.kernel.org/r/20190118175136.31341-2-mgorman@techsingularity.net
      
      Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dan Carpenter <dan.carpenter@oracle.com>
      Cc: YueHaibing <yuehaibing@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c5fbd937
    • zhengbin's avatar
      mm/filemap: pass inclusive 'end_byte' parameter to filemap_range_has_page · 35f12f0f
      zhengbin authored
      The 'end_byte' parameter of filemap_range_has_page is required to be
      inclusive, so follow the rule.
      
      Link: http://lkml.kernel.org/r/1548678679-18122-1-git-send-email-zhengbin13@huawei.com
      Fixes: 6be96d3a
      
       ("fs: return if direct I/O will trigger writeback")
      Signed-off-by: default avatarzhengbin <zhengbin13@huawei.com>
      Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarMatthew Wilcox <willy@infradead.org>
      Acked-by: default avatarChristoph Hellwig <hch@lst.de>
      Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
      Cc: Amir Goldstein <amir73il@gmail.com>
      Cc: Dave Chinner <david@fromorbit.com>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Hou Tao <houtao1@huawei.com>
      Cc: zhangyi (F) <yi.zhang@huawei.com>
      Cc: Jan Kara <jack@suse.cz>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      35f12f0f
    • Alexey Dobriyan's avatar
      mm: shuffle GFP_* flags · d71e53ce
      Alexey Dobriyan authored
      GFP_KERNEL is one of the most used constant but on archs like arm with
      fixed length instruction some constants are more equal than the others.
      Constants with tightly packed bits can be injected directly into
      instruction stream:
      
      	   0:   e3a00d33        mov     r0, #3264       ; 0xcc0
      
      Others require multiple instructions or even loading out of instruction
      stream:
      
      	   0:   e3a000c0        mov     r0, #192        ; 0xc0
      	   4:   e3400060        movt    r0, #96		; 0x60
      
      Shuffle GFP_* flags so that GFP_KERNEL/GFP_ATOMIC + __GFP_ZERO bits are
      close to each other.
      
      Savings on arm configs are ~0.1%.
      
      Link: http://lkml.kernel.org/r/20190109201838.GA9140@avx2
      
      Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
      Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d71e53ce
    • Yang Shi's avatar
      mm: swap: add comment for swap_vma_readahead · e9f59873
      Yang Shi authored
      swap_vma_readahead()'s comment is missing, just add it.
      
      Link: http://lkml.kernel.org/r/1546543673-108536-2-git-send-email-yang.shi@linux.alibaba.com
      
      Signed-off-by: default avatarYang Shi <yang.shi@linux.alibaba.com>
      Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Huang Ying <ying.huang@intel.com>
      Cc: Tim Chen <tim.c.chen@intel.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
      Cc: Hugh Dickins <hughd@google.com
      Cc: Jens Axboe <axboe@kernel.dk>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      e9f59873