From: Shakeel Butt Date: Tue, 26 May 2026 03:39:30 +0000 (-0700) Subject: memcg: int16_t for cached slab stats X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7a09fb91c285ba1b253f7c72f86cf37b373afb10;p=thirdparty%2Flinux.git memcg: int16_t for cached slab stats Currently struct obj_stock_pcp stores cached slab stats in 'int' which is 4 bytes per counter on 64-bit machines. Switch them to int16_t to shrink the cached metadata. The existing PAGE_SIZE flush in __account_obj_stock() bounds *bytes at PAGE_SIZE on 4KiB and 16KiB page archs, well within int16_t. On 64KiB pages PAGE_SIZE is well above S16_MAX so that flush never fires, and a sufficiently long run of accumulations would overflow the cache. Add an explicit S16_MAX guard before each add: when the next add would push abs(*bytes) past S16_MAX, fold the cached value into @nr and flush directly via mod_objcg_mlstate() before the accumulation. Link: https://lore.kernel.org/20260526033931.1760588-4-shakeel.butt@linux.dev Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") Signed-off-by: Shakeel Butt Tested-by: kernel test robot Reviewed-by: Harry Yoo (Oracle) Acked-by: Qi Zheng Acked-by: Muchun Song Cc: Alexandre Ghiti Cc: Johannes Weiner Cc: Joshua Hahn Cc: Michal Hocko Cc: Roman Gushchin Signed-off-by: Andrew Morton --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 8bbcc7bc42e3..ac7c99e32f99 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2032,8 +2032,8 @@ struct obj_stock_pcp { uint16_t nr_bytes; #endif int16_t node_id; - int nr_slab_reclaimable_b; - int nr_slab_unreclaimable_b; + int16_t nr_slab_reclaimable_b; + int16_t nr_slab_unreclaimable_b; struct work_struct work; unsigned long flags; @@ -3170,7 +3170,7 @@ static void __account_obj_stock(struct obj_cgroup *objcg, struct obj_stock_pcp *stock, int nr, struct pglist_data *pgdat, enum node_stat_item idx) { - int *bytes; + int16_t *bytes; /* * Though at the moment MAX_NUMNODES <= 1024 in all archs but let's make @@ -3207,21 +3207,20 @@ static void __account_obj_stock(struct obj_cgroup *objcg, bytes = (idx == NR_SLAB_RECLAIMABLE_B) ? &stock->nr_slab_reclaimable_b : &stock->nr_slab_unreclaimable_b; + /* - * Even for large object >= PAGE_SIZE, the vmstat data will still be - * cached locally at least once before pushing it out. + * Fold @nr into the cached value and decide whether to keep it cached + * or flush it directly. Cache the combined value when it fits in the + * int16_t storage and either the cache was empty (so even a value + * above PAGE_SIZE gets a chance to be canceled by a paired delta) or + * the combined value is within the PAGE_SIZE flush threshold. */ - if (!*bytes) { + nr += *bytes; + if (abs(nr) <= S16_MAX && (!*bytes || abs(nr) <= PAGE_SIZE)) { *bytes = nr; nr = 0; } else { - *bytes += nr; - if (abs(*bytes) > PAGE_SIZE) { - nr = *bytes; - *bytes = 0; - } else { - nr = 0; - } + *bytes = 0; } direct: if (nr)