From: Yang Shi shy828301@gmail.com
mainline inclusion from mainline-v5.13-rc1 commit 18bb473e5031213ebfa9a622c0b0f8cdcb8a5371 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I48N0H CVE: NA
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The number of deferred objects might get windup to an absurd number, and it results in clamp of slab objects. It is undesirable for sustaining workingset.
So shrink deferred objects proportional to priority and cap nr_deferred to twice of cache items.
The idea is borrowed from Dave Chinner's patch: https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.co...
Tested with kernel build and vfs metadata heavy workload in our production environment, no regression is spotted so far.
Link: https://lkml.kernel.org/r/20210311190845.9708-14-shy828301@gmail.com Signed-off-by: Yang Shi shy828301@gmail.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Kirill Tkhai ktkhai@virtuozzo.com Cc: Michal Hocko mhocko@suse.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.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 Reviewed-by: Tong Tiangen tongtiangen@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- mm/vmscan.c | 46 +++++++++++----------------------------------- 1 file changed, 11 insertions(+), 35 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 63e82d136712..cb830ec05fad 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -666,7 +666,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, */ nr = xchg_nr_deferred(shrinker, shrinkctl);
- total_scan = nr; if (shrinker->seeks) { delta = freeable >> priority; delta *= 4; @@ -680,37 +679,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, delta = freeable / 2; }
+ total_scan = nr >> priority; total_scan += delta; - if (total_scan < 0) { - pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n", - shrinker->scan_objects, total_scan); - total_scan = freeable; - next_deferred = nr; - } else - next_deferred = total_scan; - - /* - * We need to avoid excessive windup on filesystem shrinkers - * due to large numbers of GFP_NOFS allocations causing the - * shrinkers to return -1 all the time. This results in a large - * nr being built up so when a shrink that can do some work - * comes along it empties the entire cache due to nr >>> - * freeable. This is bad for sustaining a working set in - * memory. - * - * Hence only allow the shrinker to scan the entire cache when - * a large delta change is calculated directly. - */ - if (delta < freeable / 4) - total_scan = min(total_scan, freeable / 2); - - /* - * Avoid risking looping forever due to too large nr value: - * never try to free more than twice the estimate number of - * freeable entries. - */ - if (total_scan > freeable * 2) - total_scan = freeable * 2; + total_scan = min(total_scan, (2 * freeable));
trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, freeable, delta, total_scan, priority); @@ -749,10 +720,15 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, cond_resched(); }
- if (next_deferred >= scanned) - next_deferred -= scanned; - else - next_deferred = 0; + /* + * The deferred work is increased by any new work (delta) that wasn't + * done, decreased by old deferred work that was done now. + * + * And it is capped to two times of the freeable items. + */ + next_deferred = max_t(long, (nr + delta - scanned), 0); + next_deferred = min(next_deferred, (2 * freeable)); + /* * move the unused scan count back into the shrinker in a * manner that handles concurrent updates.