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Wed, 12 Aug 2026 23:44:25 +0000 X-Migadu-Flow: FLOW_OUT Date: Wed, 12 Aug 2026 16:44:19 -0700 From: Shakeel Butt To: Guopeng Zhang Cc: Johannes Weiner , Roman Gushchin , Vlastimil Babka , Andrew Morton , Michal Hocko , Muchun Song , Harry Yoo , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Guopeng Zhang , Ran Xiaokai Subject: Re: [PATCH] mm: memcg: fix slab over-accounting for in-object objcg metadata Message-ID: References: <20260812124858.73487-1-guopeng.zhang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260812124858.73487-1-guopeng.zhang@linux.dev> X-Rspamd-Queue-Id: 264FE120003 X-Rspam-User: X-Stat-Signature: phm9bbnphoqocno38shbo6bq8obreago X-Rspamd-Server: rspam06 X-HE-Tag: 1786578266-446421 X-HE-Meta: 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 5Og7rfdJ pXm7ZHwC/9Q6WgSLo2QRWWJ4ZRpndTR+z4mQ4U5ZAxvGDlogYcDDUaaFIxtRcxNHhhGOjUMZBZh9nXN2//KBh11DVvhhOdfmg5ngRnUI2ebyFLH2WdRMPVksm426R30jPJdSdxo6q/AympDq1nld9rfCqERD94H48OnYgtQdtw3RXzLcWARrCQU8DAfin5N931MHdZvnlSkZMK0BQGyi382Qf32rpJcv8DLMMmXwiT5++YjT6PgTHaGcQCzPAwl8nkt+SpxYZr34OZCeTFqaE9zwqmGTlM8CKKE6sbVv994CHSEtpYazq5DjsM3KasMcU61ovKv+EZqKVRnYoJhaCTEO57XkeaZNH+lSCL3QOxIzvBbY4ZoF4z2xrnYdHR0lUpWf2lDLvOHqeNjT0cz0NJbcFtwuMaRRu/LbGbTvoVPKRW/g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 12, 2026 at 08:48:58PM +0800, Guopeng Zhang wrote: > From: Guopeng Zhang > > obj_full_size() adds the size of an obj_cgroup pointer to s->size to > account for slabobj_ext storage, which normally resides outside the > object. > > Since commit a77d6d338685 ("mm/slab: place slabobj_ext metadata in > unused space within s->size"), slabobj_ext can reside in object padding > already covered by s->size. The extra charge then accounts for the same > memory twice. > > The per-slab obj_exts_in_object bit introduced by commit b5bc35ace2c5 > ("mm/slab: replace slab.stride with obj_exts_in_object") identifies this > layout. Use it to omit the extra charge only for in-object metadata. > Unlike in-object metadata, slab-leftover and separately allocated metadata > are not covered by the per-object s->size charge, so retain the existing > charge for those cases. > > Reported-by: Ran Xiaokai > Link: https://lore.kernel.org/all/20260310113804.245647-1-ranxiaokai627@163.com/ > Fixes: a77d6d338685 ("mm/slab: place slabobj_ext metadata in unused space within s->size") > Signed-off-by: Guopeng Zhang This looks good to me but would love to have Harry's comment on it.