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t=1784213020; bh=mU+AkHG+unovjoou+Gc++cD5SyJh4xwusPC7zchS0m8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FJauAJakhRvLtd584lr/GAriHLfmUjBqPUdRIv4YrgWA5IhTqvb2tRcX1o3i24R+g 2broTkPr1VeFpwXQXpsesKck8xUKjn83EjzPBr+yqgR86w4zBP2aCYT00Cyd2D2cix MPeXf+WXorOO0Rj40ZtpBDXH2RA/12A1xbXD7FbhFEUpMG5hgiCDiPukBTEedWe6UH 9hPL/878X3Rs4xlvQjToaIItSVqWLW2hOQ6RBfrZ3UtIibFGKvR8bhvbGRZyEKSLnU u9w+91zOogOw1vMlsvBhVj2vSKayZKuflTHagKlETCzG+3EdoJU4Mn4mixnFkK5pPV lqcN8AinTwW6g== Message-ID: <01aa6803-e6a7-4172-94ef-043914e2f794@kernel.org> Date: Thu, 16 Jul 2026 16:43:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 08/12] mm/slab: change struct slabobj_ext to a union Content-Language: en-US To: Suren Baghdasaryan Cc: Harry Yoo , Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> <20260715-b4-objext_split-v1-8-9a49c4ccf4c3@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D1AEB40009 X-Stat-Signature: nkfiom5tkidhnta9izst8kq5b7osapbn X-HE-Tag: 1784213020-308621 X-HE-Meta: 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 EUdtLDWk 6ikVRlE2+mZR2UZj34jAqfcE2dbLYiAVHbL3zGK72ZiwIqp19YIKB1y0xQQC13t13Ij3TKey+39nnFx/rRE9PYRAZrcGTEYjshNQyXuZgLdMKdH3VTxq84qTsn5rNjWLFbDLE6yB2/be7ECRkNWLCFpJ9/E3mWvoKAzrNSWaPNOpg7V3EWfUsEoE4xV84fgWC9GzxsgnplE+CtBTQgCeQRIKb9IU7aIusoPJ1YO/4BknpOFiD39MPgSFqRAs9qVrrz5Y2PezEt8CI4N1JHkA1lXHYiNwToBCU7CyrgWaKA6j7HSHvBdM1LmLtm8qC+YdYJaiqyIESCzlbobXOj2b/NOgLWw8bgpZMxAfvslWyPvgbhnQX+tP7yqjNM/VN5fS+jdCR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/16/26 06:11, Suren Baghdasaryan wrote: > On Wed, Jul 15, 2026 at 3:11 AM Vlastimil Babka (SUSE) > wrote: >> No functional change intended, the layout is still effectively static. >> >> Signed-off-by: Vlastimil Babka (SUSE) > > This is much cleaner than what I was preparing. Nicely done! > > Reviewed-by: Suren Baghdasaryan Thanks! >> --- >> mm/slab.h | 41 +++++++++++++++++++++++++++++++++-------- >> mm/slub.c | 17 +++++++++-------- >> 2 files changed, 42 insertions(+), 16 deletions(-) >> >> diff --git a/mm/slab.h b/mm/slab.h >> index 3ad9777ad600..359ab8caf61e 100644 >> --- a/mm/slab.h >> +++ b/mm/slab.h >> @@ -554,14 +554,34 @@ static inline bool need_kmalloc_no_objext(void) >> * if MEMCG_DATA_OBJEXTS is set. >> */ >> struct slabobj_ext { > > Perhaps we should add a comment here stating that every element of > this union should be pointer-sized? > OK, how about this? --- a/mm/slab.h +++ b/mm/slab.h @@ -550,10 +550,14 @@ static inline bool need_kmalloc_no_objext(void) } /* - * Extended information for slab objects stored as an array in page->memcg_data - * if MEMCG_DATA_OBJEXTS is set. + * Extended information for slab objects stored as a pointer to an array in + * slab->obj_exts (aliasing page->memcg_data) if MEMCG_DATA_OBJEXTS is set. */ struct slabobj_ext { + /* + * All elements of the union should be pointer-sized to avoid memory + * waste + */ union { #ifdef CONFIG_MEMCG struct obj_cgroup *_objcg;