From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-118.mta0.migadu.com [91.218.175.118]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 36429453A28 for ; Wed, 12 Aug 2026 13:48:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.118 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786542521; cv=none; b=R3HLFwWxLhEovqbX9Ze0P1tkm1GQlAkvOhpUECEMx89M5/bHf04doxJDiq5bxJC9wJX0ZYldu3i4gIRvWR6SlWVEobKYjKKhxa7lIp5hj9ro1J9+yX4otRsy29BWeZFJ+MfKRPauDhVBm/xn+feTKqi2ncFe/EA0IVkr/f/SFzg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786542521; c=relaxed/simple; bh=ASMCgRYWFh1U8hGKVOolQ/aTQ/PK231J3u3FwxsWacs=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=b/XkMOjzJmzc/H/P32nNH9RIXGTjq6NwYv16wnMgYyI1wFjpcbtO0DOb0CcprT4b/BwBCj/LjamJhLvVFrnH9KIWQJXIYBN9MCn9uS4yWb1ONYNxO2SNOH77OtEQf4YtDSuLNk603GnEfDABMdYvCo4x12eXB6A9ILPAJOarHzg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=bqt6VLL2; arc=none smtp.client-ip=91.218.175.118 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="bqt6VLL2" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=ASMCgRYWFh1U8hGKVOolQ/aTQ/PK231J3u3FwxsWacs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1786542517; v=1; x=1787147317; b=bqt6VLL2oPMWtajSw0sxl/NU0Mo2Oiu8rit8fZeSxMtlJERaEfHNKZKZGumb5o1F/v0QRCK2 qUUzXNLihvi8GGJFN+FA5creF05Y21skfBl4r/uq1Rk1GluMrGOYCYW47E7+tLQu4EMtBrQmm9x 8hNvs/6pH89NGSVYK7fZ3GIY= X-Envelope-To: linux-kernel@vger.kernel.org Received: from [192.168.1.116] (111.162.215.50) by smtp.migadu.com with ESMTPS id 18dd0f5011e94cb8; Wed, 12 Aug 2026 13:48:37 +0000 X-Migadu-Flow: FLOW_OUT Message-ID: <3ab5e2cb-0660-4b20-9e67-cb47e17ae554@linux.dev> Date: Wed, 12 Aug 2026 21:48:26 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: cui.tao@linux.dev, Michal Hocko , Shakeel Butt , 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 To: Guopeng Zhang , Johannes Weiner , Roman Gushchin , Vlastimil Babka , Andrew Morton References: <20260812124858.73487-1-guopeng.zhang@linux.dev> From: Tao Cui In-Reply-To: <20260812124858.73487-1-guopeng.zhang@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 在 2026/8/12 20:48, Guopeng Zhang 写道: > 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 > --- > mm/memcontrol.c | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d1312441a02b..aef480f46891 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3526,12 +3526,16 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size) > refill_obj_stock(objcg, size, true); > } > > -static inline size_t obj_full_size(struct kmem_cache *s) > +static inline size_t obj_full_size(struct kmem_cache *s, struct slab *slab) > { > /* > * For each accounted object there is an extra space which is used > - * to store obj_cgroup membership. Charge it too. > + * to store obj_cgroup membership. Charge it too, unless it is stored > + * in object padding already covered by s->size. > */ > + if (obj_exts_in_object(slab)) > + return s->size; > + > return s->size + sizeof(struct obj_cgroup *); > } > > @@ -3539,7 +3543,6 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > gfp_t flags, unsigned int slab_alloc_flags, > size_t size, void **p) > { > - size_t obj_size = obj_full_size(s); > struct obj_cgroup *objcg; > struct slab *slab; > size_t i; > @@ -3580,6 +3583,7 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > unsigned long obj_exts; > struct slabobj_ext *obj_ext; > struct obj_stock_pcp *stock; > + size_t obj_size; > > slab = virt_to_slab(p[i]); > > @@ -3590,6 +3594,8 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > continue; > } > > + obj_size = obj_full_size(s, slab); > + > /* > * if we fail and size is 1, memcg_alloc_abort_single() will > * just free the object, which is ok as we have not assigned > @@ -3632,7 +3638,7 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, > void **p, int objects, unsigned long obj_exts) > { > - size_t obj_size = obj_full_size(s); > + size_t obj_size = obj_full_size(s, slab); > > for (int i = 0; i < objects; i++) { > struct obj_cgroup *objcg; > > base-commit: e7f630142df2afccce90555e4972e60008222311 Reviewed-by: Tao Cui