mm, vmstat: remove zone and node double accounting by approximating retries

The number of LRU pages, dirty pages and writeback pages must be
accounted for on both zones and nodes because of the reclaim retry
logic, compaction retry logic and highmem calculations all depending on
per-zone stats.

Many lowmem allocations are immune from OOM kill due to a check in
__alloc_pages_may_oom for (ac->high_zoneidx < ZONE_NORMAL) since commit
03668b3ceb0c ("oom: avoid oom killer for lowmem allocations").  The
exception is costly high-order allocations or allocations that cannot
fail.  If the __alloc_pages_may_oom avoids OOM-kill for low-order lowmem
allocations then it would fall through to __alloc_pages_direct_compact.

This patch will blindly retry reclaim for zone-constrained allocations
in should_reclaim_retry up to MAX_RECLAIM_RETRIES.  This is not ideal
but without per-zone stats there are not many alternatives.  The impact
it that zone-constrained allocations may delay before considering the
OOM killer.

As there is no guarantee enough memory can ever be freed to satisfy
compaction, this patch avoids retrying compaction for zone-contrained
allocations.

In combination, that means that the per-node stats can be used when
deciding whether to continue reclaim using a rough approximation.  While
it is possible this will make the wrong decision on occasion, it will
not infinite loop as the number of reclaim attempts is capped by
MAX_RECLAIM_RETRIES.

The final step is calculating the number of dirtyable highmem pages.  As
those calculations only care about the global count of file pages in
highmem.  This patch uses a global counter used instead of per-zone
stats as it is sufficient.

In combination, this allows the per-zone LRU and dirty state counters to
be removed.

[mgorman@techsingularity.net: fix acct_highmem_file_pages()]
  Link: http://lkml.kernel.org/r/1468853426-12858-4-git-send-email-mgorman@techsingularity.netLink: http://lkml.kernel.org/r/1467970510-21195-35-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Suggested by: Michal Hocko <mhocko@kernel.org>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 43 insertions, 12 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 03e67f2dfdaa..f1b5a0bc11f2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3402,6 +3402,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
 {
         struct zone *zone;
         struct zoneref *z;
+        pg_data_t *current_pgdat = NULL;
 
         /*
          * Make sure we converge to OOM if we cannot make any progress
@@ -3411,27 +3412,56 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
                 return false;
 
         /*
-         * Keep reclaiming pages while there is a chance this will lead somewhere.
-         * If none of the target zones can satisfy our allocation request even
-         * if all reclaimable pages are considered then we are screwed and have
-         * to go OOM.
+         * Blindly retry lowmem allocation requests that are often ignored by
+         * the OOM killer up to MAX_RECLAIM_RETRIES as we not have a reliable
+         * and fast means of calculating reclaimable, dirty and writeback pages
+         * in eligible zones.
+         */
+        if (ac->high_zoneidx < ZONE_NORMAL)
+                goto out;
+
+        /*
+         * Keep reclaiming pages while there is a chance this will lead
+         * somewhere.  If none of the target zones can satisfy our allocation
+         * request even if all reclaimable pages are considered then we are
+         * screwed and have to go OOM.
          */
         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
                                         ac->nodemask) {
                 unsigned long available;
                 unsigned long reclaimable;
+                int zid;
 
-                available = reclaimable = zone_reclaimable_pages(zone);
+                if (current_pgdat == zone->zone_pgdat)
+                        continue;
+
+                current_pgdat = zone->zone_pgdat;
+                available = reclaimable = pgdat_reclaimable_pages(current_pgdat);
                 available -= DIV_ROUND_UP(no_progress_loops * available,
                                           MAX_RECLAIM_RETRIES);
-                available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
+
+                /* Account for all free pages on eligible zones */
+                for (zid = 0; zid <= zone_idx(zone); zid++) {
+                        struct zone *acct_zone = &current_pgdat->node_zones[zid];
+
+                        available += zone_page_state_snapshot(acct_zone, NR_FREE_PAGES);
+                }
 
                 /*
                  * Would the allocation succeed if we reclaimed the whole
-                 * available?
+                 * available? This is approximate because there is no
+                 * accurate count of reclaimable pages per zone.
                  */
-                if (__zone_watermark_ok(zone, order, min_wmark_pages(zone),
-                                ac_classzone_idx(ac), alloc_flags, available)) {
+                for (zid = 0; zid <= zone_idx(zone); zid++) {
+                        struct zone *check_zone = &current_pgdat->node_zones[zid];
+                        unsigned long estimate;
+
+                        estimate = min(check_zone->managed_pages, available);
+                        if (!__zone_watermark_ok(check_zone, order,
+                                        min_wmark_pages(check_zone), ac_classzone_idx(ac),
+                                        alloc_flags, estimate))
+                                continue;
+
                         /*
                          * If we didn't make any progress and have a lot of
                          * dirty + writeback pages then we should wait for
@@ -3441,15 +3471,16 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
                         if (!did_some_progress) {
                                 unsigned long write_pending;
 
-                                write_pending = zone_page_state_snapshot(zone,
-                                                        NR_ZONE_WRITE_PENDING);
+                                write_pending =
+                                        node_page_state(current_pgdat, NR_WRITEBACK) +
+                                        node_page_state(current_pgdat, NR_FILE_DIRTY);
 
                                 if (2 * write_pending > reclaimable) {
                                         congestion_wait(BLK_RW_ASYNC, HZ/10);
                                         return true;
                                 }
                         }
-
+out:
                         /*
                          * Memory allocation/reclaim might be called from a WQ
                          * context and the current implementation of the WQ