From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D98A93E92B0; Fri, 17 Jul 2026 10:00:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784282436; cv=none; b=Zc5hq6TiRNeZUN4XCU4v/9hMM9vUAAiqzUTV4vMsm3xW0S5Aj3NZA9u1g3EZ30U8EyKoDBgp+g39GxcOyO5vUv20RBXa30vJviV2AnBITrCf7hKz37UMKf8WyF+yYdAkiKks+zYBLTpmclnVSnJz84nBVcJ4XDec8+xPmsG6lbM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784282436; c=relaxed/simple; bh=21SvuiXGb63/yGdgyprvkQaVhJu+r+1ZurssCMSiB0M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VbfwYQ4C2YX+ecm+0RajwrIdCCbFF9jLVhysgFqhonHl7ZFJ8HTUT8oQEfX98k2gRc6U63hfsbZ3Xj7WtPyfWqnsGtGi4rdK+SXFeUqlDgqtC7ZJY7laxp5ZG4pv6GgF8TSU73FveFuKBq/n11GywBdM5ZPKhbMpPKfxwzSggAg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WsUNWYE9; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WsUNWYE9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6AA891F000E9; Fri, 17 Jul 2026 10:00:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784282434; bh=DF6HG8VRcKlp7PWGtfJlKS/XAeUYbsad4fOuP/0NSHk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WsUNWYE9hbLye9jbYYTr2L2WVzCZINOuxbayrBrAXK6Cz01pKIezn8IdD+EGo6Xr/ I8FDVn+XXdV/1lo1cFHQtucXPasWDUXFmAkbuQkm2JTGqk553ZHiEE5CUuUtIBhVmG SL0tepNCQIHdD3Y2yXGVmYT0n2hfE8XukEKWE+8VLpq+eOKNZkdtCuyBSpf16rHiQ2 kUfF5oomr8F3VZWrLQCiYuVzuBOzyJPLnJU5INb/t9ycS0l9iCDNN9WFCTT5UXU+2f RluCZoa83CNb9wPfHjcWQEBYZ9mFQOUxAySO60TB1iSqDh6cZc3U+vKgnXU52PePPd 6S2lIKsoBFEDA== Message-ID: <976e4d7b-24d6-4047-a405-e86c2feb45d3@kernel.org> Date: Fri, 17 Jul 2026 12:00:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 05/12] mm/slab: abstract slabobj_ext.objcg access Content-Language: en-US To: Harry Yoo , Suren Baghdasaryan , Roman Gushchin , Ye Liu Cc: Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Stephen Brennan , SeongJae Park , Omar Sandoval References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> <20260715-b4-objext_split-v1-5-9a49c4ccf4c3@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/15/26 12:10, Vlastimil Babka (SUSE) wrote: > In preparation for changes to the structure, abstract access to the > objcg field with a slab_obj_ext_objcgp() function. > Rename the field to _objcg to make an unexpected direct access a compile > error. > > No functional change intended. > > Signed-off-by: Vlastimil Babka (SUSE) Hm sashiko finds [1] that this is breaks tools/mm/show_page_info.py But I think it was already buggy. get_memcg_info() is supposed to return memcg info for a page but in case of MEMCG_DATA_OBJEXTS there's no such info for the whole page, there is only for individual slab objects and it doesn't know which object so it effectively gets the first one. I think it should just stop handling MEMCG_DATA_OBJEXTS, but that's a fix that should be sent unrelated to this series. There's also tools/cgroup/memcg_slabinfo.py and that I think has been already broken with memalloc profiling as it assuems slab.memcg_data is still a raw struct obj_cgroup * and not struct slabobj_ext. I think it will be easier to fix it at once to handle the layout after this series than trying to fix it first to handle the pre-series layout and then update it with every relevant change. [1] https://sashiko.dev/#/patchset/20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org?part=5 > --- > mm/kfence/core.c | 2 +- > mm/memcontrol.c | 23 +++++++++++++++-------- > mm/slab.h | 9 ++++++++- > mm/slub.c | 2 +- > 4 files changed, 25 insertions(+), 11 deletions(-) > > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index 6577bd76954e..717e8baf7e5d 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -1249,7 +1249,7 @@ void __kfence_free(void *addr) > struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); > > #ifdef CONFIG_MEMCG > - KFENCE_WARN_ON(meta->obj_exts.objcg); > + KFENCE_WARN_ON(*slab_obj_ext_objcgp(&meta->obj_exts)); > #endif > /* > * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4e427286a88a..6303a2b1a9d0 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2865,6 +2865,7 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) > */ > unsigned long obj_exts; > struct slabobj_ext *obj_ext; > + struct obj_cgroup *objcg; > > obj_exts = slab_obj_exts(slab); > if (!obj_exts) > @@ -2872,9 +2873,8 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) > > get_slab_obj_exts(obj_exts); > obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p); > - if (obj_ext->objcg) { > - struct obj_cgroup *objcg = obj_ext->objcg; > - > + objcg = *slab_obj_ext_objcgp(obj_ext); > + if (objcg) { > put_slab_obj_exts(obj_exts); > return obj_cgroup_memcg(objcg); > } > @@ -3577,6 +3577,7 @@ 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; > + struct obj_cgroup **objcgp; > > slab = virt_to_slab(p[i]); > > @@ -3612,10 +3613,15 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > unlock_stock(stock); > > obj_exts = slab_obj_exts(slab); > + > get_slab_obj_exts(obj_exts); > + > obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]); > + objcgp = slab_obj_ext_objcgp(obj_ext); > + > obj_cgroup_get(objcg); > - obj_ext->objcg = objcg; > + *objcgp = objcg; > + > put_slab_obj_exts(obj_exts); > } > > @@ -3628,16 +3634,17 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, > size_t obj_size = obj_full_size(s); > > for (int i = 0; i < objects; i++) { > - struct obj_cgroup *objcg; > + struct obj_cgroup **objcgp, *objcg; > struct slabobj_ext *obj_ext; > struct obj_stock_pcp *stock; > > obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]); > - objcg = obj_ext->objcg; > - if (!objcg) > + objcgp = slab_obj_ext_objcgp(obj_ext); > + if (!*objcgp) > continue; > > - obj_ext->objcg = NULL; > + objcg = *objcgp; > + *objcgp = NULL; > > stock = trylock_stock(); > __refill_obj_stock(objcg, stock, obj_size, true); > diff --git a/mm/slab.h b/mm/slab.h > index 36d067d6e7c0..789bd292075f 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -555,7 +555,7 @@ static inline bool need_kmalloc_no_objext(void) > */ > struct slabobj_ext { > #ifdef CONFIG_MEMCG > - struct obj_cgroup *objcg; > + struct obj_cgroup *_objcg; > #endif > #ifdef CONFIG_MEM_ALLOC_PROFILING > union codetag_ref ref; > @@ -661,6 +661,13 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts, > return kasan_reset_tag(obj_ext); > } > > +#ifdef CONFIG_MEMCG > +static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ext) > +{ > + return &obj_ext->_objcg; > +} > +#endif > + > int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > gfp_t gfp, unsigned int alloc_flags); > > diff --git a/mm/slub.c b/mm/slub.c > index 5e3f53bcd0d3..48e10198a3ce 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2523,7 +2523,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags) > if (obj_exts) { > get_slab_obj_exts(obj_exts); > obj_ext = slab_obj_ext(s, slab, obj_exts, p); > - if (unlikely(obj_ext->objcg)) { > + if (unlikely(*slab_obj_ext_objcgp(obj_ext))) { > put_slab_obj_exts(obj_exts); > return true; > } >