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References: <20201210160020.21562-1-vbabka@suse.cz>
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From:   Joonsoo Kim <js1304@gmail.com>
Date:   Fri, 11 Dec 2020 10:17:05 +0900
Message-ID: <CAAmzW4M0qS7XBQ1L+iWLWoLh2R30EeLaPy=5Ncw-Uz17bdKukg@mail.gmail.com>
Subject: Re: [PATCH] mm, slab, slub: clear the slab_cache field when freeing page
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Matthew Wilcox <willy@infradead.org>
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2020=EB=85=84 12=EC=9B=94 11=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 1:00, =
Vlastimil Babka <vbabka@suse.cz>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> The page allocator expects that page->mapping is NULL for a page being fr=
eed.
> SLAB and SLUB use the slab_cache field which is in union with mapping, bu=
t
> before freeing the page, the field is referenced with the "mapping" name =
when
> set to NULL.
>
> It's IMHO more correct (albeit functionally the same) to use the slab_cac=
he
> name as that's the field we use in SL*B, and document why we clear it in =
a
> comment (we don't clear fields such as s_mem or freelist, as page allocat=
or
> doesn't care about those). While using the 'mapping' name would automagic=
ally
> keep the code correct if the unions in struct page changed, such changes =
should
> be done consciously and needed changes evaluated - the comment should hel=
p with
> that.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>