Commit 5515061d authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds

mm: throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is...

mm: throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage

If swap is backed by network storage such as NBD, there is a risk that a
large number of reclaimers can hang the system by consuming all
PF_MEMALLOC reserves.  To avoid these hangs, the administrator must tune
min_free_kbytes in advance which is a bit fragile.

This patch throttles direct reclaimers if half the PF_MEMALLOC reserves
are in use.  If the system is routinely getting throttled the system
administrator can increase min_free_kbytes so degradation is smoother but
the system will keep running.
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7f338fe4
......@@ -705,6 +705,7 @@ typedef struct pglist_data {
range, including holes */
int node_id;
wait_queue_head_t kswapd_wait;
wait_queue_head_t pfmemalloc_wait;
struct task_struct *kswapd; /* Protected by lock_memory_hotplug() */
int kswapd_max_order;
enum zone_type classzone_idx;
......
......@@ -4389,6 +4389,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
pgdat_resize_init(pgdat);
pgdat->nr_zones = 0;
init_waitqueue_head(&pgdat->kswapd_wait);
init_waitqueue_head(&pgdat->pfmemalloc_wait);
pgdat->kswapd_max_order = 0;
pgdat_page_cgroup_init(pgdat);
......
......@@ -2112,6 +2112,80 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
return 0;
}
static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
{
struct zone *zone;
unsigned long pfmemalloc_reserve = 0;
unsigned long free_pages = 0;
int i;
bool wmark_ok;
for (i = 0; i <= ZONE_NORMAL; i++) {
zone = &pgdat->node_zones[i];
pfmemalloc_reserve += min_wmark_pages(zone);
free_pages += zone_page_state(zone, NR_FREE_PAGES);
}
wmark_ok = free_pages > pfmemalloc_reserve / 2;
/* kswapd must be awake if processes are being throttled */
if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
pgdat->classzone_idx = min(pgdat->classzone_idx,
(enum zone_type)ZONE_NORMAL);
wake_up_interruptible(&pgdat->kswapd_wait);
}
return wmark_ok;
}
/*
* Throttle direct reclaimers if backing storage is backed by the network
* and the PFMEMALLOC reserve for the preferred node is getting dangerously
* depleted. kswapd will continue to make progress and wake the processes
* when the low watermark is reached
*/
static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
nodemask_t *nodemask)
{
struct zone *zone;
int high_zoneidx = gfp_zone(gfp_mask);
pg_data_t *pgdat;
/*
* Kernel threads should not be throttled as they may be indirectly
* responsible for cleaning pages necessary for reclaim to make forward
* progress. kjournald for example may enter direct reclaim while
* committing a transaction where throttling it could forcing other
* processes to block on log_wait_commit().
*/
if (current->flags & PF_KTHREAD)
return;
/* Check if the pfmemalloc reserves are ok */
first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
pgdat = zone->zone_pgdat;
if (pfmemalloc_watermark_ok(pgdat))
return;
/*
* If the caller cannot enter the filesystem, it's possible that it
* is due to the caller holding an FS lock or performing a journal
* transaction in the case of a filesystem like ext[3|4]. In this case,
* it is not safe to block on pfmemalloc_wait as kswapd could be
* blocked waiting on the same lock. Instead, throttle for up to a
* second before continuing.
*/
if (!(gfp_mask & __GFP_FS)) {
wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat), HZ);
return;
}
/* Throttle until kswapd wakes the process */
wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat));
}
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
gfp_t gfp_mask, nodemask_t *nodemask)
{
......@@ -2131,6 +2205,15 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
.gfp_mask = sc.gfp_mask,
};
throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
/*
* Do not enter reclaim if fatal signal is pending. 1 is returned so
* that the page allocator does not consider triggering OOM
*/
if (fatal_signal_pending(current))
return 1;
trace_mm_vmscan_direct_reclaim_begin(order,
sc.may_writepage,
gfp_mask);
......@@ -2275,8 +2358,13 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
return balanced_pages >= (present_pages >> 2);
}
/* is kswapd sleeping prematurely? */
static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
/*
* Prepare kswapd for sleeping. This verifies that there are no processes
* waiting in throttle_direct_reclaim() and that watermarks have been met.
*
* Returns true if kswapd is ready to sleep
*/
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
int classzone_idx)
{
int i;
......@@ -2285,7 +2373,21 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
return true;
return false;
/*
* There is a potential race between when kswapd checks its watermarks
* and a process gets throttled. There is also a potential race if
* processes get throttled, kswapd wakes, a large process exits therby
* balancing the zones that causes kswapd to miss a wakeup. If kswapd
* is going to sleep, no process should be sleeping on pfmemalloc_wait
* so wake them now if necessary. If necessary, processes will wake
* kswapd and get throttled again
*/
if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
wake_up(&pgdat->pfmemalloc_wait);
return false;
}
/* Check the watermark levels */
for (i = 0; i <= classzone_idx; i++) {
......@@ -2318,9 +2420,9 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
* must be balanced
*/
if (order)
return !pgdat_balanced(pgdat, balanced, classzone_idx);
return pgdat_balanced(pgdat, balanced, classzone_idx);
else
return !all_zones_ok;
return all_zones_ok;
}
/*
......@@ -2546,6 +2648,16 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
}
}
/*
* If the low watermark is met there is no need for processes
* to be throttled on pfmemalloc_wait as they should not be
* able to safely make forward progress. Wake them
*/
if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
pfmemalloc_watermark_ok(pgdat))
wake_up(&pgdat->pfmemalloc_wait);
if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
break; /* kswapd: all done */
/*
......@@ -2647,7 +2759,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
}
/*
* Return the order we were reclaiming at so sleeping_prematurely()
* Return the order we were reclaiming at so prepare_kswapd_sleep()
* makes a decision on the order we were last reclaiming at. However,
* if another caller entered the allocator slow path while kswapd
* was awake, order will remain at the higher level
......@@ -2667,7 +2779,7 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
/* Try to sleep for a short interval */
if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
remaining = schedule_timeout(HZ/10);
finish_wait(&pgdat->kswapd_wait, &wait);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
......@@ -2677,7 +2789,7 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
* After a short sleep, check if it was a premature sleep. If not, then
* go fully to sleep until explicitly woken up.
*/
if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
/*
......
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