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mm, slab, slub: clear the slab_cache field when freeing page

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The page allocator expects that page->mapping is NULL for a page being
freed.  SLAB and SLUB use the slab_cache field which is in union with
mapping, but 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_cache 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 allocator doesn't care about those).  While using the 'mapping' name
would automagically keep the code correct if the unions in struct page
changed, such changes should be done consciously and needed changes
evaluated - the comment should help with that.

Link: https://lkml.kernel.org/r/20201210160020.21562-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2020-12-14 19:04:29 -08:00 committed by Linus Torvalds
parent a47fc51d8e
commit 0c06dd7551
2 changed files with 4 additions and 3 deletions
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3
mm/slab.c
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@ -1399,7 +1399,8 @@ static void kmem_freepages(struct kmem_cache *cachep, struct page *page)
__ClearPageSlabPfmemalloc(page);
__ClearPageSlab(page);
page_mapcount_reset(page);
page->mapping = NULL;
/* In union with page->mapping where page allocator expects NULL */
page->slab_cache = NULL;
if (current->reclaim_state)
current->reclaim_state->reclaimed_slab += 1 << order;

4
mm/slub.c
View File

@ -1836,8 +1836,8 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
__ClearPageSlabPfmemalloc(page);
__ClearPageSlab(page);
page->mapping = NULL;
/* In union with page->mapping where page allocator expects NULL */
page->slab_cache = NULL;
if (current->reclaim_state)
current->reclaim_state->reclaimed_slab += pages;
unaccount_slab_page(page, order, s);