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From: Muchun Song In-Reply-To: <20260522011908.1669332-3-shakeel.butt@linux.dev> Date: Fri, 22 May 2026 14:27:41 +0800 Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Harry Yoo , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260522011908.1669332-1-shakeel.butt@linux.dev> <20260522011908.1669332-3-shakeel.butt@linux.dev> To: Shakeel Butt X-Migadu-Flow: FLOW_OUT X-Stat-Signature: zhcqyb86xqqs91nw7kz6etnsudofikfd X-Rspamd-Queue-Id: 934EC1C0004 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1779431299-146096 X-HE-Meta: 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 nNmHHC77 OgFpf4GLCIiNZmK6kkrsth8576RwKKFpIBEBgncBpyHmuF2+bHbDne5qGhd3WcJFNyJs1+h8bPQ2k6+QnTNg0DaXKdMKDcKw43wXz8AKWjkHgC3CjnOtngQWcgE9ctNOaG3Se0EKtO7+T5GBfd0Jc+PszTB6QNWo+5bt6Uc+CqfSQifdIPXLNxaJO2CDXgifsJ52a6EIy3WttIFeREGNRpv+OObw65HUko2LzTPv0ZO1tLtXG8pbngWTFnq5jLHVA+FLqlLK4I0ieGV05a67PBfFhet8kt4CD8AQxzzDpzobuSc9WrhbwSud/jMaF7Ti4pSS/MqII94UwAL0Vg+IXuswKqZDeXZHoJVASFVPkt/i1y4faRIle9oZIWruZjXniJD1RAH59PdHso6ZwbEf9pylpYQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On May 22, 2026, at 09:19, Shakeel Butt = wrote: >=20 > 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. >=20 > 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 > =3D=3D U16_MAX, but on 256KiB pages PAGE_SIZE - 1 =3D=3D 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. >=20 > Accumulate the new total in an 'unsigned int' local, then: >=20 > 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 <=3D 64KiB. >=20 > 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. >=20 > 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) Acked-by: Muchun Song Thanks.