diff options
| author | Johannes Weiner <hannes@cmpxchg.org> | 2025-04-16 09:45:39 -0400 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-04-17 20:10:09 -0700 |
| commit | 38448181459e24257b40d5258afdbaa3565e8cfc (patch) | |
| tree | b46dc11af491d3160e106ab1911911e77bb7ab20 /mm | |
| parent | 2db93a896fec7109302598cf45de3831340d9f53 (diff) | |
mm: vmscan: restore high-cpu watermark safety in kswapd
Vlastimil points out that commit a211c6550efc ("mm: page_alloc:
defrag_mode kswapd/kcompactd watermarks") switched kswapd from
zone_watermark_ok_safe() to the standard, percpu-cached version of reading
free pages, thus dropping the watermark safety precautions for systems
with high CPU counts (e.g. >212 cpus on 64G). Restore them.
Since zone_watermark_ok_safe() is no longer the right interface, and this
was the last caller of the function anyway, open-code the
zone_page_state_snapshot() conditional and delete the function.
Link: https://lkml.kernel.org/r/20250416135142.778933-2-hannes@cmpxchg.org
Fixes: a211c6550efc ("mm: page_alloc: defrag_mode kswapd/kcompactd watermarks")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/page_alloc.c | 12 | ||||
| -rw-r--r-- | mm/vmscan.c | 21 |
2 files changed, 19 insertions, 14 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e506e365d6f1..5669baf2a6fe 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3470,18 +3470,6 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order, return false; } -bool zone_watermark_ok_safe(struct zone *z, unsigned int order, - unsigned long mark, int highest_zoneidx) -{ - long free_pages = zone_page_state(z, NR_FREE_PAGES); - - if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark) - free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES); - - return __zone_watermark_ok(z, order, mark, highest_zoneidx, 0, - free_pages); -} - #ifdef CONFIG_NUMA int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE; diff --git a/mm/vmscan.c b/mm/vmscan.c index b620d74b0f66..cc422ad830d6 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -6736,6 +6736,7 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx) * meet watermarks. */ for_each_managed_zone_pgdat(zone, pgdat, i, highest_zoneidx) { + enum zone_stat_item item; unsigned long free_pages; if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) @@ -6748,9 +6749,25 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx) * blocks to avoid polluting allocator fallbacks. */ if (defrag_mode) - free_pages = zone_page_state(zone, NR_FREE_PAGES_BLOCKS); + item = NR_FREE_PAGES_BLOCKS; else - free_pages = zone_page_state(zone, NR_FREE_PAGES); + item = NR_FREE_PAGES; + + /* + * When there is a high number of CPUs in the system, + * the cumulative error from the vmstat per-cpu cache + * can blur the line between the watermarks. In that + * case, be safe and get an accurate snapshot. + * + * TODO: NR_FREE_PAGES_BLOCKS moves in steps of + * pageblock_nr_pages, while the vmstat pcp threshold + * is limited to 125. On many configurations that + * counter won't actually be per-cpu cached. But keep + * things simple for now; revisit when somebody cares. + */ + free_pages = zone_page_state(zone, item); + if (zone->percpu_drift_mark && free_pages < zone->percpu_drift_mark) + free_pages = zone_page_state_snapshot(zone, item); if (__zone_watermark_ok(zone, order, mark, highest_zoneidx, 0, free_pages)) |