diff options
| author | Shakeel Butt <shakeel.butt@linux.dev> | 2026-05-25 20:39:29 -0700 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-05-28 21:32:03 -0700 |
| commit | c9a1aa3aeef3cc852b382d714f0f1718fd68cc66 (patch) | |
| tree | 9376ea45f318df4826ceb766488d721f636f9fda /mm | |
| parent | a48a944f102d99e934839a78b815fd8792a7d346 (diff) | |
| download | linux-next-history-c9a1aa3aeef3cc852b382d714f0f1718fd68cc66.tar.gz | |
memcg: uint16_t for nr_bytes in obj_stock_pcp
Currently struct obj_stock_pcp stores nr_bytes in an 'unsigned int' which
is 4 bytes on 64-bit machines. Switch the field to uint16_t to shrink the
per-CPU cache.
The kernel supports PAGE_SIZE_4KB, _8KB, _16KB, _32KB, _64KB and _256KB
(see HAVE_PAGE_SIZE_* in arch/Kconfig). After the PAGE_SIZE-aligned flush
in __refill_obj_stock(), the sub-page remainder fits in uint16_t up
through 64KiB pages where PAGE_SIZE - 1 == U16_MAX, but on 256KiB pages
PAGE_SIZE - 1 == 0x3FFFF exceeds U16_MAX. The accumulator also needs to
stay within uint16_t between page-aligned flushes on 64KiB pages where
PAGE_SIZE itself is U16_MAX + 1.
Accumulate the new total in an 'unsigned int' local, then on PAGE_SHIFT <=
16 flush whenever the accumulator would hit U16_MAX; together with the
existing allow_uncharge flush at PAGE_SIZE this keeps the uint16_t safe.
On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on hexagon and powerpc
44x, both 32-bit), uint16_t cannot represent the sub-page remainder.
Define obj_stock_bytes_t as 'unsigned int' on those archs so nr_bytes can
hold the full remainder and the normal page-boundary flush in
__refill_obj_stock() and the page extraction in drain_obj_stock() both
work correctly.
The single-cache-line layout target only applies to PAGE_SHIFT <= 16;
those archs are 32-bit embedded and not the optimization target.
Link: https://lore.kernel.org/20260526033931.1760588-3-shakeel.butt@linux.dev
Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Tested-by: kernel test robot <oliver.sang@intel.com>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: Muchun Song <muchun.song@linux.dev>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memcontrol.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e983fa590af8c..8bbcc7bc42e3d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2020,8 +2020,17 @@ static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { struct obj_stock_pcp { local_trylock_t lock; - unsigned int nr_bytes; struct obj_cgroup *cached_objcg; +#if PAGE_SHIFT > 16 + /* + * On rare archs with 256KiB base page size (hexagon and powerpc 44x) + * keep nr_bytes to unsigned int as uint16_t cannot represent the full + * sub-page remainder. + */ + unsigned int nr_bytes; +#else + uint16_t nr_bytes; +#endif int16_t node_id; int nr_slab_reclaimable_b; int nr_slab_unreclaimable_b; @@ -3334,6 +3343,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, bool allow_uncharge) { unsigned int nr_pages = 0; + unsigned int stock_nr_bytes; if (!stock) { nr_pages = nr_bytes >> PAGE_SHIFT; @@ -3342,21 +3352,24 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, goto out; } + stock_nr_bytes = stock->nr_bytes; if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ drain_obj_stock(stock); obj_cgroup_get(objcg); - stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) + stock_nr_bytes = atomic_read(&objcg->nr_charged_bytes) ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; WRITE_ONCE(stock->cached_objcg, objcg); allow_uncharge = true; /* Allow uncharge when objcg changes */ } - stock->nr_bytes += nr_bytes; + stock_nr_bytes += nr_bytes; - if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) { - nr_pages = stock->nr_bytes >> PAGE_SHIFT; - stock->nr_bytes &= (PAGE_SIZE - 1); + if ((allow_uncharge && (stock_nr_bytes > PAGE_SIZE)) || + stock_nr_bytes > U16_MAX) { + nr_pages = stock_nr_bytes >> PAGE_SHIFT; + stock_nr_bytes &= (PAGE_SIZE - 1); } + stock->nr_bytes = stock_nr_bytes; out: if (nr_pages) |