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: Mel 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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7f338fe454
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5515061d22
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@ -705,6 +705,7 @@ typedef struct pglist_data {
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range, including holes */
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int node_id;
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wait_queue_head_t kswapd_wait;
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wait_queue_head_t pfmemalloc_wait;
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struct task_struct *kswapd; /* Protected by lock_memory_hotplug() */
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int kswapd_max_order;
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enum zone_type classzone_idx;
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@ -4389,6 +4389,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
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pgdat_resize_init(pgdat);
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pgdat->nr_zones = 0;
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init_waitqueue_head(&pgdat->kswapd_wait);
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init_waitqueue_head(&pgdat->pfmemalloc_wait);
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pgdat->kswapd_max_order = 0;
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pgdat_page_cgroup_init(pgdat);
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128
mm/vmscan.c
128
mm/vmscan.c
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@ -2112,6 +2112,80 @@ out:
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return 0;
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}
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static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
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{
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struct zone *zone;
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unsigned long pfmemalloc_reserve = 0;
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unsigned long free_pages = 0;
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int i;
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bool wmark_ok;
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for (i = 0; i <= ZONE_NORMAL; i++) {
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zone = &pgdat->node_zones[i];
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pfmemalloc_reserve += min_wmark_pages(zone);
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free_pages += zone_page_state(zone, NR_FREE_PAGES);
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}
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wmark_ok = free_pages > pfmemalloc_reserve / 2;
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/* kswapd must be awake if processes are being throttled */
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if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
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pgdat->classzone_idx = min(pgdat->classzone_idx,
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(enum zone_type)ZONE_NORMAL);
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wake_up_interruptible(&pgdat->kswapd_wait);
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}
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return wmark_ok;
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}
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/*
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* Throttle direct reclaimers if backing storage is backed by the network
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* and the PFMEMALLOC reserve for the preferred node is getting dangerously
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* depleted. kswapd will continue to make progress and wake the processes
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* when the low watermark is reached
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*/
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static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
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nodemask_t *nodemask)
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{
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struct zone *zone;
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int high_zoneidx = gfp_zone(gfp_mask);
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pg_data_t *pgdat;
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/*
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* Kernel threads should not be throttled as they may be indirectly
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* responsible for cleaning pages necessary for reclaim to make forward
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* progress. kjournald for example may enter direct reclaim while
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* committing a transaction where throttling it could forcing other
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* processes to block on log_wait_commit().
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*/
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if (current->flags & PF_KTHREAD)
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return;
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/* Check if the pfmemalloc reserves are ok */
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first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
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pgdat = zone->zone_pgdat;
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if (pfmemalloc_watermark_ok(pgdat))
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return;
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/*
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* If the caller cannot enter the filesystem, it's possible that it
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* is due to the caller holding an FS lock or performing a journal
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* transaction in the case of a filesystem like ext[3|4]. In this case,
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* it is not safe to block on pfmemalloc_wait as kswapd could be
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* blocked waiting on the same lock. Instead, throttle for up to a
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* second before continuing.
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*/
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if (!(gfp_mask & __GFP_FS)) {
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wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
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pfmemalloc_watermark_ok(pgdat), HZ);
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return;
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}
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/* Throttle until kswapd wakes the process */
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wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
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pfmemalloc_watermark_ok(pgdat));
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}
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unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
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gfp_t gfp_mask, nodemask_t *nodemask)
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{
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@ -2131,6 +2205,15 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
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.gfp_mask = sc.gfp_mask,
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};
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throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
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/*
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* Do not enter reclaim if fatal signal is pending. 1 is returned so
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* that the page allocator does not consider triggering OOM
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*/
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if (fatal_signal_pending(current))
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return 1;
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trace_mm_vmscan_direct_reclaim_begin(order,
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sc.may_writepage,
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gfp_mask);
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@ -2275,8 +2358,13 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
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return balanced_pages >= (present_pages >> 2);
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}
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/* is kswapd sleeping prematurely? */
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static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
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/*
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* Prepare kswapd for sleeping. This verifies that there are no processes
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* waiting in throttle_direct_reclaim() and that watermarks have been met.
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*
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* Returns true if kswapd is ready to sleep
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*/
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static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
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int classzone_idx)
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{
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int i;
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@ -2285,7 +2373,21 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
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/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
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if (remaining)
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return true;
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return false;
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/*
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* There is a potential race between when kswapd checks its watermarks
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* and a process gets throttled. There is also a potential race if
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* processes get throttled, kswapd wakes, a large process exits therby
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* balancing the zones that causes kswapd to miss a wakeup. If kswapd
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* is going to sleep, no process should be sleeping on pfmemalloc_wait
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* so wake them now if necessary. If necessary, processes will wake
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* kswapd and get throttled again
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*/
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if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
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wake_up(&pgdat->pfmemalloc_wait);
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return false;
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}
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/* Check the watermark levels */
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for (i = 0; i <= classzone_idx; i++) {
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@ -2318,9 +2420,9 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
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* must be balanced
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*/
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if (order)
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return !pgdat_balanced(pgdat, balanced, classzone_idx);
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return pgdat_balanced(pgdat, balanced, classzone_idx);
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else
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return !all_zones_ok;
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return all_zones_ok;
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}
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/*
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@ -2546,6 +2648,16 @@ loop_again:
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}
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}
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/*
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* If the low watermark is met there is no need for processes
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* to be throttled on pfmemalloc_wait as they should not be
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* able to safely make forward progress. Wake them
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*/
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if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
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pfmemalloc_watermark_ok(pgdat))
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wake_up(&pgdat->pfmemalloc_wait);
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if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
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break; /* kswapd: all done */
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/*
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@ -2647,7 +2759,7 @@ out:
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}
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/*
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* Return the order we were reclaiming at so sleeping_prematurely()
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* Return the order we were reclaiming at so prepare_kswapd_sleep()
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* makes a decision on the order we were last reclaiming at. However,
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* if another caller entered the allocator slow path while kswapd
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* was awake, order will remain at the higher level
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@ -2667,7 +2779,7 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
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prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
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/* Try to sleep for a short interval */
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if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
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if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
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remaining = schedule_timeout(HZ/10);
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finish_wait(&pgdat->kswapd_wait, &wait);
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prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
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* After a short sleep, check if it was a premature sleep. If not, then
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* go fully to sleep until explicitly woken up.
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*/
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if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
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if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
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trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
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/*
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