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From: Qi Zheng In-Reply-To: <20260522011908.1669332-3-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: C594580005 X-Rspamd-Server: rspam03 X-Stat-Signature: 893dhyyaabwp8yr1kxr5nb5dh3mbnf9e X-HE-Tag: 1779416649-707456 X-HE-Meta: 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 QvKgbhBg H2BiteJdjvfhlfzTr6Ut1YEjY/Zzoa5lLGGApkR4dL3eTzmnNR2dvAg15fCC6adoWNa8YQi+uBXRrqyR79Nepna3UyJVsKP3WRtN9WG61ZBCzzWuGf+zuThvEp+++qMZMLKObyirfb3JVmbVkhb/6A8Q5Gjk8UYw6U0TMicNuQhCCQTrz0nCAeG7oET1IVUyGNee4d1W8dBt/8449mMIULVmFN0O+dFa4QlxFDJ9XL/BeALU4MSxGSd74GuxSYNtnyu6diP807CSPk2YqwpKBIcmqYYRBUGcloqJTIAMuv8Smqr42hV+FCKwouTcihExy6gcg0hsU6JqpMSiiOteNUlQ9x1DtVAF6v38dH5MosUz2JH1fkhX6PXgicw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/22/26 9:19 AM, Shakeel Butt wrote: > 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: > > 1. 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 PAGE_SIZE <= 64KiB. > > 2. On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on hexagon and > powerpc 44x), push any sub-page remainder above U16_MAX into > objcg->nr_charged_bytes via atomic_add before storing back, so > the store cannot silently truncate. The PAGE_SHIFT > 16 guard > folds the branch out at compile time on smaller page sizes. > > Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") > Tested-by: kernel test robot > Signed-off-by: Shakeel Butt > Reviewed-by: Harry Yoo (Oracle) > --- > > Changes since v1: > - Collected tags > - Rearrange fields of obj_stock_pcp (David Laight) > - Fix comparison operator (Harry) > > mm/memcontrol.c | 33 +++++++++++++++++++++++++++------ > 1 file changed, 27 insertions(+), 6 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d7c162946719..e4f00a8159d5 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2019,8 +2019,8 @@ 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; > + uint16_t nr_bytes; > int16_t node_id; > int nr_slab_reclaimable_b; > int nr_slab_unreclaimable_b; > @@ -3331,6 +3331,7 @@ 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; > @@ -3339,21 +3340,41 @@ 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; > + > + /* Since stock->nr_bytes is uint16_t, don't refill >= U16_MAX */ ^ should also be changed to: don't refill > U16_MAX ? Otherwise: Acked-by: Qi Zheng Thanks! > + 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); > + > + /* > + * On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on > + * hexagon and powerpc 44x), the sub-page remainder can > + * still exceed U16_MAX. Push the excess back to > + * objcg->nr_charged_bytes so the store into uint16_t > + * cannot silently truncate; folded out at compile time > + * on smaller page sizes. > + */ > + if (PAGE_SHIFT > 16 && stock_nr_bytes > U16_MAX) { > + unsigned int kept = stock_nr_bytes & U16_MAX; > > - if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) { > - nr_pages = stock->nr_bytes >> PAGE_SHIFT; > - stock->nr_bytes &= (PAGE_SIZE - 1); > + atomic_add(stock_nr_bytes - kept, > + &objcg->nr_charged_bytes); > + stock_nr_bytes = kept; > + } > } > + stock->nr_bytes = stock_nr_bytes; > > out: > if (nr_pages)