1. 14 May, 2019 1 commit
    • Ira Weiny's avatar
      mm/gup: change GUP fast to use flags rather than a write 'bool' · 73b0140b
      Ira Weiny authored
      To facilitate additional options to get_user_pages_fast() change the
      singular write parameter to be gup_flags.
      
      This patch does not change any functionality.  New functionality will
      follow in subsequent patches.
      
      Some of the get_user_pages_fast() call sites were unchanged because they
      already passed FOLL_WRITE or 0 for the write parameter.
      
      NOTE: It was suggested to change the ordering of the get_user_pages_fast()
      arguments to ensure that callers were converted.  This breaks the current
      GUP call site convention of having the returned pages be the final
      parameter.  So the suggestion was rejected.
      
      Link: http://lkml.kernel.org/r/20190328084422.29911-4-ira.weiny@intel.com
      Link: http://lkml.kernel.org/r/20190317183438.2057-4-ira.weiny@intel.com
      
      Signed-off-by: default avatarIra Weiny <ira.weiny@intel.com>
      Reviewed-by: default avatarMike Marshall <hubcap@omnibond.com>
      Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Dan Williams <dan.j.williams@intel.com>
      Cc: "David S. Miller" <davem@davemloft.net>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: James Hogan <jhogan@kernel.org>
      Cc: Jason Gunthorpe <jgg@ziepe.ca>
      Cc: John Hubbard <jhubbard@nvidia.com>
      Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Michal Hocko <mhocko@kernel.org>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Ralf Baechle <ralf@linux-mips.org>
      Cc: Rich Felker <dalias@libc.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      73b0140b
  2. 04 Jan, 2019 1 commit
    • Linus Torvalds's avatar
      Remove 'type' argument from access_ok() function · 96d4f267
      Linus Torvalds authored
      Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
      of the user address range verification function since we got rid of the
      old racy i386-only code to walk page tables by hand.
      
      It existed because the original 80386 would not honor the write protect
      bit when in kernel mode, so you had to do COW by hand before doing any
      user access.  But we haven't supported that in a long time, and these
      days the 'type' argument is a purely historical artifact.
      
      A discussion about extending 'user_access_begin()' to do the range
      checking resulted this patch, because there is no way we're going to
      move the old VERIFY_xyz interface to that model.  And it's best done at
      the end of the merge window when I've done most of my merges, so let's
      just get this done once and for all.
      
      This patch was mostly done with a sed-script, with manual fix-ups for
      the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.
      
      There were a couple of notable cases:
      
       - csk...
      96d4f267
  3. 14 Apr, 2018 1 commit
  4. 02 Nov, 2017 1 commit
    • Greg Kroah-Hartman's avatar
      License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
      Greg Kroah-Hartman authored
      Many source files in the tree are missing licensing information, which
      makes it harder for compliance tools to determine the correct license.
      
      By default all files without license information are under the default
      license of the kernel, which is GPL version 2.
      
      Update the files which contain no license information with the 'GPL-2.0'
      SPDX license identifier.  The SPDX identifier is a legally binding
      shorthand, which can be used instead of the full boiler plate text.
      
      This patch is based on work done by Thomas Gleixner and Kate Stewart and
      Philippe Ombredanne.
      
      How this work was done:
      
      Patches were generated and checked against linux-4.14-rc6 for a subset of
      the use cases:
       - file had no licensing information it it.
       - file was a */uapi/* one with no licensing information in it,
       - file was a */uapi/* one with existing licensing information,
      
      Further patches will be generated in subsequent months to fix up cases
      where non-standard...
      b2441318
  5. 18 Oct, 2016 1 commit
  6. 17 Mar, 2016 1 commit
    • Joonsoo Kim's avatar
      mm: introduce page reference manipulation functions · fe896d18
      Joonsoo Kim authored
      
      
      The success of CMA allocation largely depends on the success of
      migration and key factor of it is page reference count.  Until now, page
      reference is manipulated by direct calling atomic functions so we cannot
      follow up who and where manipulate it.  Then, it is hard to find actual
      reason of CMA allocation failure.  CMA allocation should be guaranteed
      to succeed so finding offending place is really important.
      
      In this patch, call sites where page reference is manipulated are
      converted to introduced wrapper function.  This is preparation step to
      add tracepoint to each page reference manipulation function.  With this
      facility, we can easily find reason of CMA allocation failure.  There is
      no functional change in this patch.
      
      In addition, this patch also converts reference read sites.  It will
      help a second step that renames page._count to something else and
      prevents later attempt to direct access to it (Suggested by Andrew).
      Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Acked-by: default avatarMichal Nazarewicz <mina86@mina86.com>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Mel Gorman <mgorman@techsingularity.net>
      Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
      Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      fe896d18
  7. 16 Feb, 2016 1 commit
    • Dave Hansen's avatar
      mm/gup: Switch all callers of get_user_pages() to not pass tsk/mm · d4edcf0d
      Dave Hansen authored
      
      
      We will soon modify the vanilla get_user_pages() so it can no
      longer be used on mm/tasks other than 'current/current->mm',
      which is by far the most common way it is called.  For now,
      we allow the old-style calls, but warn when they are used.
      (implemented in previous patch)
      
      This patch switches all callers of:
      
      	get_user_pages()
      	get_user_pages_unlocked()
      	get_user_pages_locked()
      
      to stop passing tsk/mm so they will no longer see the warnings.
      Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
      Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Brian Gerst <brgerst@gmail.com>
      Cc: Dave Hansen <dave@sr71.net>
      Cc: Denys Vlasenko <dvlasenk@redhat.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
      Cc: Vlastimil Babka <vbabka@suse.cz>
      Cc: jack@suse.cz
      Cc: linux-mm@kvack.org
      Link: http://lkml.kernel.org/r/20160212210156.113E9407@viggo.jf.intel.com
      
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
      d4edcf0d
  8. 16 Jan, 2016 2 commits
    • Kirill A. Shutemov's avatar
      mips, thp: remove infrastructure for handling splitting PMDs · b2787370
      Kirill A. Shutemov authored
      
      
      With new refcounting we don't need to mark PMDs splitting.  Let's drop
      code to handle this.
      
      pmdp_splitting_flush() is not needed too: on splitting PMD we will do
      pmdp_clear_flush() + set_pte_at().  pmdp_clear_flush() will do IPI as
      needed for fast_gup.
      Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Sasha Levin <sasha.levin@oracle.com>
      Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
      Cc: Jerome Marchand <jmarchan@redhat.com>
      Cc: Vlastimil Babka <vbabka@suse.cz>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
      Cc: Steve Capper <steve.capper@linaro.org>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: Michal Hocko <mhocko@suse.cz>
      Cc: Christoph Lameter <cl@linux.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>
      b2787370
    • Kirill A. Shutemov's avatar
      mm: drop tail page refcounting · ddc58f27
      Kirill A. Shutemov authored
      
      
      Tail page refcounting is utterly complicated and painful to support.
      
      It uses ->_mapcount on tail pages to store how many times this page is
      pinned.  get_page() bumps ->_mapcount on tail page in addition to
      ->_count on head.  This information is required by split_huge_page() to
      be able to distribute pins from head of compound page to tails during
      the split.
      
      We will need ->_mapcount to account PTE mappings of subpages of the
      compound page.  We eliminate need in current meaning of ->_mapcount in
      tail pages by forbidding split entirely if the page is pinned.
      
      The only user of tail page refcounting is THP which is marked BROKEN for
      now.
      
      Let's drop all this mess.  It makes get_page() and put_page() much
      simpler.
      Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
      Tested-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
      Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Acked-by: default avatarJerome Marchand <jmarchan@redhat.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
      Cc: Steve Capper <steve.capper@linaro.org>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: Michal Hocko <mhocko@suse.cz>
      Cc: Christoph Lameter <cl@linux.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>
      ddc58f27
  9. 12 Feb, 2015 1 commit
  10. 18 Dec, 2014 1 commit
  11. 24 Nov, 2014 1 commit
  12. 26 Aug, 2013 1 commit
  13. 01 Feb, 2013 1 commit
  14. 27 Aug, 2012 1 commit
  15. 07 Dec, 2011 1 commit
  16. 02 Nov, 2011 2 commits
    • Andrea Arcangeli's avatar
      thp: share get_huge_page_tail() · b35a35b5
      Andrea Arcangeli authored
      
      
      This avoids duplicating the function in every arch gup_fast.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: David Gibson <david@gibson.dropbear.id.au>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: David Miller <davem@davemloft.net>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      b35a35b5
    • Andrea Arcangeli's avatar
      mm: thp: tail page refcounting fix · 70b50f94
      Andrea Arcangeli authored
      
      
      Michel while working on the working set estimation code, noticed that
      calling get_page_unless_zero() on a random pfn_to_page(random_pfn)
      wasn't safe, if the pfn ended up being a tail page of a transparent
      hugepage under splitting by __split_huge_page_refcount().
      
      He then found the problem could also theoretically materialize with
      page_cache_get_speculative() during the speculative radix tree lookups
      that uses get_page_unless_zero() in SMP if the radix tree page is freed
      and reallocated and get_user_pages is called on it before
      page_cache_get_speculative has a chance to call get_page_unless_zero().
      
      So the best way to fix the problem is to keep page_tail->_count zero at
      all times.  This will guarantee that get_page_unless_zero() can never
      succeed on any tail page.  page_tail->_mapcount is guaranteed zero and
      is unused for all tail pages of a compound page, so we can simply
      account the tail page references there and transfer them to
      tail_page->_count in __split_huge_page_refcount() (in addition to the
      head_page->_mapcount).
      
      While debugging this s/_count/_mapcount/ change I also noticed get_page is
      called by direct-io.c on pages returned by get_user_pages.  That wasn't
      entirely safe because the two atomic_inc in get_page weren't atomic.  As
      opposed to other get_user_page users like secondary-MMU page fault to
      establish the shadow pagetables would never call any superflous get_page
      after get_user_page returns.  It's safer to make get_page universally safe
      for tail pages and to use get_page_foll() within follow_page (inside
      get_user_pages()).  get_page_foll() is safe to do the refcounting for tail
      pages without taking any locks because it is run within PT lock protected
      critical sections (PT lock for pte and page_table_lock for
      pmd_trans_huge).
      
      The standard get_page() as invoked by direct-io instead will now take
      the compound_lock but still only for tail pages.  The direct-io paths
      are usually I/O bound and the compound_lock is per THP so very
      finegrined, so there's no risk of scalability issues with it.  A simple
      direct-io benchmarks with all lockdep prove locking and spinlock
      debugging infrastructure enabled shows identical performance and no
      overhead.  So it's worth it.  Ideally direct-io should stop calling
      get_page() on pages returned by get_user_pages().  The spinlock in
      get_page() is already optimized away for no-THP builds but doing
      get_page() on tail pages returned by GUP is generally a rare operation
      and usually only run in I/O paths.
      
      This new refcounting on page_tail->_mapcount in addition to avoiding new
      RCU critical sections will also allow the working set estimation code to
      work without any further complexity associated to the tail page
      refcounting with THP.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Reported-by: default avatarMichel Lespinasse <walken@google.com>
      Reviewed-by: default avatarMichel Lespinasse <walken@google.com>
      Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: David Gibson <david@gibson.dropbear.id.au>
      Cc: <stable@kernel.org>
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      70b50f94
  17. 14 Jan, 2011 3 commits
  18. 03 Feb, 2010 1 commit
  19. 20 Jun, 2009 1 commit
    • Linus Torvalds's avatar
      x86: don't use 'access_ok()' as a range check in get_user_pages_fast() · 7f818906
      Linus Torvalds authored
      
      
      It's really not right to use 'access_ok()', since that is meant for the
      normal "get_user()" and "copy_from/to_user()" accesses, which are done
      through the TLB, rather than through the page tables.
      
      Why? access_ok() does both too few, and too many checks.  Too many,
      because it is meant for regular kernel accesses that will not honor the
      'user' bit in the page tables, and because it honors the USER_DS vs
      KERNEL_DS distinction that we shouldn't care about in GUP.  And too few,
      because it doesn't do the 'canonical' check on the address on x86-64,
      since the TLB will do that for us.
      
      So instead of using a function that isn't meant for this, and does
      something else and much more complicated, just do the real rules: we
      don't want the range to overflow, and on x86-64, we want it to be a
      canonical low address (on 32-bit, all addresses are canonical).
      Acked-by: default avatarIngo Molnar <mingo@elte.hu>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      7f818906
  20. 19 Jun, 2009 1 commit
    • Ingo Molnar's avatar
      perf_counter, x86: Improve interactions with fast-gup · 0c871971
      Ingo Molnar authored
      
      
      Improve a few details in perfcounter call-chain recording that
      makes use of fast-GUP:
      
      - Use ACCESS_ONCE() to observe the pte value. ptes are fundamentally
        racy and can be changed on another CPU, so we have to be careful
        about how we access them. The PAE branch is already careful with
        read-barriers - but the non-PAE and 64-bit side needs an
        ACCESS_ONCE() to make sure the pte value is observed only once.
      
      - make the checks a bit stricter so that we can feed it any kind of
        cra^H^H^H user-space input ;-)
      Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      0c871971
  21. 15 Jun, 2009 1 commit
  22. 10 Apr, 2009 1 commit
  23. 29 Oct, 2008 1 commit
    • Harvey Harrison's avatar
      x86: two trivial sparse annotations · 9352f569
      Harvey Harrison authored
      
      
      Impact: fewer sparse warnings, no functional changes
      
      arch/x86/kernel/vsmp_64.c:87:14: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:87:14:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:87:14:    got void *[assigned] address
      arch/x86/kernel/vsmp_64.c:88:22: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:88:22:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:88:22:    got void *
      arch/x86/kernel/vsmp_64.c:100:23: warning: incorrect type in argument 2 (different address spaces)
      arch/x86/kernel/vsmp_64.c:100:23:    expected void volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:100:23:    got void *
      arch/x86/kernel/vsmp_64.c:101:23: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:101:23:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:101:23:    got void *
      arch/x86/mm/gup.c:235:6: warning: incorrect type in argument 1 (different base types)
      arch/x86/mm/gup.c:235:6:    expected void const volatile [noderef] <asn:1>*<noident>
      arch/x86/mm/gup.c:235:6:    got unsigned long [unsigned] [assigned] start
      Signed-off-by: default avatarHarvey Harrison <harvey.harrison@gmail.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      9352f569
  24. 13 Oct, 2008 1 commit
  25. 29 Jul, 2008 1 commit
  26. 26 Jul, 2008 2 commits
    • Nick Piggin's avatar
      x86: support 1GB hugepages with get_user_pages_lockless() · 652ea695
      Nick Piggin authored
      
      Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andi Kleen <andi@firstfloor.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      652ea695
    • Nick Piggin's avatar
      x86: lockless get_user_pages_fast() · 8174c430
      Nick Piggin authored
      
      
      Implement get_user_pages_fast without locking in the fastpath on x86.
      
      Do an optimistic lockless pagetable walk, without taking mmap_sem or any
      page table locks or even mmap_sem.  Page table existence is guaranteed by
      turning interrupts off (combined with the fact that we're always looking
      up the current mm, means we can do the lockless page table walk within the
      constraints of the TLB shootdown design).  Basically we can do this
      lockless pagetable walk in a similar manner to the way the CPU's pagetable
      walker does not have to take any locks to find present ptes.
      
      This patch (combined with the subsequent ones to convert direct IO to use
      it) was found to give about 10% performance improvement on a 2 socket 8
      core Intel Xeon system running an OLTP workload on DB2 v9.5
      
       "To test the effects of the patch, an OLTP workload was run on an IBM
        x3850 M2 server with 2 processors (quad-core Intel Xeon processors at
        2.93 GHz) using IBM DB2 v9.5 running Linux 2.6.24rc7 kernel.  Comparing
        runs with and without the patch resulted in an overall performance
        benefit of ~9.8%.  Correspondingly, oprofiles showed that samples from
        __up_read and __down_read routines that is seen during thread contention
        for system resources was reduced from 2.8% down to .05%.  Monitoring the
        /proc/vmstat output from the patched run showed that the counter for
        fast_gup contained a very high number while the fast_gup_slow value was
        zero."
      
      (fast_gup is the old name for get_user_pages_fast, fast_gup_slow is a
      counter we had for the number of times the slowpath was invoked).
      
      The main reason for the improvement is that DB2 has multiple threads each
      issuing direct-IO.  Direct-IO uses get_user_pages, and thus the threads
      contend the mmap_sem cacheline, and can also contend on page table locks.
      
      I would anticipate larger performance gains on larger systems, however I
      think DB2 uses an adaptive mix of threads and processes, so it could be
      that thread contention remains pretty constant as machine size increases.
      In which case, we stuck with "only" a 10% gain.
      
      The downside of using get_user_pages_fast is that if there is not a pte
      with the correct permissions for the access, we end up falling back to
      get_user_pages and so the get_user_pages_fast is a bit of extra work.
      However this should not be the common case in most performance critical
      code.
      
      [akpm@linux-foundation.org: coding-style fixes]
      [akpm@linux-foundation.org: build fix]
      [akpm@linux-foundation.org: Kconfig fix]
      [akpm@linux-foundation.org: Makefile fix/cleanup]
      [akpm@linux-foundation.org: warning fix]
      Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
      Cc: Dave Kleikamp <shaggy@austin.ibm.com>
      Cc: Andy Whitcroft <apw@shadowen.org>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andi Kleen <andi@firstfloor.org>
      Cc: Dave Kleikamp <shaggy@austin.ibm.com>
      Cc: Badari Pulavarty <pbadari@us.ibm.com>
      Cc: Zach Brown <zach.brown@oracle.com>
      Cc: Jens Axboe <jens.axboe@oracle.com>
      Reviewed-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8174c430