The patch titled
vmscan: properly account for the number of page cache pages zone_reclaim() can reclaim
has been added to the -mm tree. Its filename is
vmscan-properly-account-for-the-number-of-page-cache-pages-zone_reclaim-can-reclaim.patch
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Subject: vmscan: properly account for the number of page cache pages zone_reclaim() can reclaim
From: Mel Gorman <mel@xxxxxxxxx>
A bug was brought to my attention against a distro kernel but it affects
mainline and I believe problems like this have been reported in various
guises on the mailing lists although I don't have specific examples at the
moment.
The reported problem was that malloc() stalled for a long time (minutes in
some cases) if a large tmpfs mount was occupying a large percentage of
memory overall. The pages did not get cleaned or reclaimed by
zone_reclaim() because the zone_reclaim_mode was unsuitable, but the lists
are uselessly scanned frequencly making the CPU spin at near 100%.
This patchset intends to address that bug and bring the behaviour of
zone_reclaim() more in line with expectations which were noticed during
investigation. It is based on top of mmotm and takes advantage of
Kosaki's work with respect to zone_reclaim().
Patch 1 fixes the heuristics that zone_reclaim() uses to determine if the
scan should go ahead. The broken heuristic is what was causing the
malloc() stall as it uselessly scanned the LRU constantly. Currently,
zone_reclaim is assuming zone_reclaim_mode is 1 and historically it
could not deal with tmpfs pages at all. This fixes up the heuristic so
that an unnecessary scan is more likely to be correctly avoided.
Patch 2 notes that zone_reclaim() returning a failure automatically means
the zone is marked full. This is not always true. It could have
failed because the GFP mask or zone_reclaim_mode were unsuitable.
Patch 3 introduces a counter zreclaim_failed that will increment each
time the zone_reclaim scan-avoidance heuristics fail. If that
counter is rapidly increasing, then zone_reclaim_mode should be
set to 0 as a temporarily resolution and a bug reported because
the scan-avoidance heuristic is still broken.
This patch:
On NUMA machines, the administrator can configure zone_reclaim_mode that
is a more targetted form of direct reclaim. On machines with large NUMA
distances for example, a zone_reclaim_mode defaults to 1 meaning that
clean unmapped pages will be reclaimed if the zone watermarks are not
being met.
There is a heuristic that determines if the scan is worthwhile but the
problem is that the heuristic is not being properly applied and is
basically assuming zone_reclaim_mode is 1 if it is enabled. The lack of
proper detection can manfiest as high CPU usage as the LRU list is scanned
uselessly.
Historically, once enabled it was depending on NR_FILE_PAGES which may
include swapcache pages that the reclaim_mode cannot deal with. Patch
vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim.patch by
Kosaki Motohiro noted that zone_page_state(zone, NR_FILE_PAGES) included
pages that were not file-backed such as swapcache and made a calculation
based on the inactive, active and mapped files. This is far superior when
zone_reclaim==1 but if RECLAIM_SWAP is set, then NR_FILE_PAGES is a
reasonable starting figure.
This patch alters how zone_reclaim() works out how many pages it might be
able to reclaim given the current reclaim_mode. If RECLAIM_SWAP is set in
the reclaim_mode it will either consider NR_FILE_PAGES as potential
candidates or else use NR_{IN}ACTIVE}_PAGES-NR_FILE_MAPPED to discount
swapcache and other non-file-backed pages. If RECLAIM_WRITE is not set,
then NR_FILE_DIRTY number of pages are not candidates. If RECLAIM_SWAP is
not set, then NR_FILE_MAPPED are not.
[kosaki.motohiro@xxxxxxxxxxxxxx: Estimate unmapped pages minus tmpfs pages]
[fengguang.wu@xxxxxxxxx: Fix underflow problem in Kosaki's estimate]
Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 41 insertions(+), 7 deletions(-)
diff -puN mm/vmscan.c~vmscan-properly-account-for-the-number-of-page-cache-pages-zone_reclaim-can-reclaim mm/vmscan.c
--- a/mm/vmscan.c~vmscan-properly-account-for-the-number-of-page-cache-pages-zone_reclaim-can-reclaim
+++ a/mm/vmscan.c
@@ -2356,6 +2356,44 @@ int sysctl_min_unmapped_ratio = 1;
*/
int sysctl_min_slab_ratio = 5;
+static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
+{
+ unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
+ unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
+ zone_page_state(zone, NR_ACTIVE_FILE);
+
+ /*
+ * It's possible for there to be more file mapped pages than
+ * accounted for by the pages on the file LRU lists because
+ * tmpfs pages accounted for as ANON can also be FILE_MAPPED
+ */
+ return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
+}
+
+/* Work out how many page cache pages we can reclaim in this reclaim_mode */
+static long zone_pagecache_reclaimable(struct zone *zone)
+{
+ long nr_pagecache_reclaimable;
+ long delta = 0;
+
+ /*
+ * If RECLAIM_SWAP is set, then all file pages are considered
+ * potentially reclaimable. Otherwise, we have to worry about
+ * pages like swapcache and zone_unmapped_file_pages() provides
+ * a better estimate
+ */
+ if (zone_reclaim_mode & RECLAIM_SWAP)
+ nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
+ else
+ nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
+
+ /* If we can't clean pages, remove dirty pages from consideration */
+ if (!(zone_reclaim_mode & RECLAIM_WRITE))
+ delta += zone_page_state(zone, NR_FILE_DIRTY);
+
+ return nr_pagecache_reclaimable;
+}
+
/*
* Try to free up some pages from this zone through reclaim.
*/
@@ -2390,9 +2428,7 @@ static int __zone_reclaim(struct zone *z
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
- if (zone_page_state(zone, NR_FILE_PAGES) -
- zone_page_state(zone, NR_FILE_MAPPED) >
- zone->min_unmapped_pages) {
+ if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
/*
* Free memory by calling shrink zone with increasing
* priorities until we have enough memory freed.
@@ -2450,10 +2486,8 @@ int zone_reclaim(struct zone *zone, gfp_
* if less than a specified percentage of the zone is used by
* unmapped file backed pages.
*/
- if (zone_page_state(zone, NR_FILE_PAGES) -
- zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
- && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
- <= zone->min_slab_pages)
+ if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
+ zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
return 0;
if (zone_is_all_unreclaimable(zone))
_
Patches currently in -mm which might be from mel@xxxxxxxxx are
origin.patch
linux-next.patch
vmscan-low-order-lumpy-reclaim-also-should-use-pageout_io_sync.patch
mm-alloc_large_system_hash-check-order.patch
page-allocator-replace-__alloc_pages_internal-with-__alloc_pages_nodemask.patch
page-allocator-do-not-sanity-check-order-in-the-fast-path.patch
page-allocator-do-not-sanity-check-order-in-the-fast-path-fix.patch
page-allocator-do-not-check-numa-node-id-when-the-caller-knows-the-node-is-valid.patch
page-allocator-check-only-once-if-the-zonelist-is-suitable-for-the-allocation.patch
page-allocator-break-up-the-allocator-entry-point-into-fast-and-slow-paths.patch
page-allocator-move-check-for-disabled-anti-fragmentation-out-of-fastpath.patch
page-allocator-calculate-the-preferred-zone-for-allocation-only-once.patch
page-allocator-calculate-the-preferred-zone-for-allocation-only-once-fix.patch
page-allocator-calculate-the-migratetype-for-allocation-only-once.patch
page-allocator-calculate-the-alloc_flags-for-allocation-only-once.patch
page-allocator-remove-a-branch-by-assuming-__gfp_high-==-alloc_high.patch
page-allocator-inline-__rmqueue_smallest.patch
page-allocator-inline-buffered_rmqueue.patch
page-allocator-inline-__rmqueue_fallback.patch
page-allocator-do-not-call-get_pageblock_migratetype-more-than-necessary.patch
page-allocator-do-not-disable-interrupts-in-free_page_mlock.patch
page-allocator-do-not-setup-zonelist-cache-when-there-is-only-one-node.patch
page-allocator-do-not-check-for-compound-pages-during-the-page-allocator-sanity-checks.patch
page-allocator-use-allocation-flags-as-an-index-to-the-zone-watermark.patch
page-allocator-use-allocation-flags-as-an-index-to-the-zone-watermark-replace-the-watermark-related-union-in-struct-zone-with-a-watermark-array.patch
page-allocator-update-nr_free_pages-only-as-necessary.patch
page-allocator-update-nr_free_pages-only-as-necessary-fix.patch
page-allocator-get-the-pageblock-migratetype-without-disabling-interrupts.patch
page-allocator-use-a-pre-calculated-value-instead-of-num_online_nodes-in-fast-paths.patch
page-allocator-use-a-pre-calculated-value-instead-of-num_online_nodes-in-fast-paths-do-not-override-definition-of-node_set_online-with-macro.patch
page-allocator-slab-use-nr_online_nodes-to-check-for-a-numa-platform.patch
page-allocator-move-free_page_mlock-to-page_allocc.patch
page-allocator-sanity-check-order-in-the-page-allocator-slow-path.patch
mm-use-alloc_pages_exact-in-alloc_large_system_hash-to-avoid-duplicated-logic.patch
mm-introduce-pagehuge-for-testing-huge-gigantic-pages-update.patch
page-allocator-warn-if-__gfp_nofail-is-used-for-a-large-allocation.patch
mm-pm-freezer-disable-oom-killer-when-tasks-are-frozen.patch
page-allocator-use-integer-fields-lookup-for-gfp_zone-and-check-for-errors-in-flags-passed-to-the-page-allocator.patch
page-allocator-use-integer-fields-lookup-for-gfp_zone-and-check-for-errors-in-flags-passed-to-the-page-allocator-fix-gfp-zone-patch.patch
page-allocator-clean-up-functions-related-to-pages_min.patch
oom-move-oom_adj-value-from-task_struct-to-mm_struct.patch
oom-avoid-unnecessary-mm-locking-and-scanning-for-oom_disable.patch
oom-invoke-oom-killer-for-__gfp_nofail.patch
page-allocator-clear-n_high_memory-map-before-se-set-it-again.patch
mm-add-a-gfp-translate-script-to-help-understand-page-allocation-failure-reports.patch
mm-add-a-gfp-translate-script-to-help-understand-page-allocation-failure-reports-fix.patch
vmscan-properly-account-for-the-number-of-page-cache-pages-zone_reclaim-can-reclaim.patch
vmscan-do-not-unconditionally-treat-zones-that-fail-zone_reclaim-as-full.patch
vmscan-count-the-number-of-times-zone_reclaim-scans-and-fails.patch
add-debugging-aid-for-memory-initialisation-problems.patch
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