mm/slab: add cache_ and slab_needs_objcg() helpers

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Slabs of some caches never need the objcg part of struct slabobj_ext.
Introduce helpers to query this for a cache or a slab.

Introduce SLAB_MAY_ACCOUNT flag that is currently only internal and all
caches have it set except:

- KMALLOC_NORMAL caches, as long as KMALLOC_RECLAIM caches are separate
- KMALLOC_NO_OBJ_EXT caches, if they exist

For named caches we currently can't derive SLAB_MAY_ACCOUNT from
SLAB_ACCOUNT because some caches might be created without SLAB_ACCOUNT
and then used both with and without __GFP_ACCOUNT concurrently,
allocating obj_ext arrays on demand. So just add the SLAB_MAY_ACCOUNT
to all kmem caches, unless kmem accounting is disabled.

This can be improved later by finding out all caches used with
__GFP_ACCOUNT, creating them with the SLAB_MAY_ACCOUNT flag explicitly,
and then ignoring __GFP_ACCOUNT for all other caches (possibly with a
warning).

To make the evaluation of slab_needs_objcg() faster in the allocation
and free fast paths, add a obj_exts_needs_objcg flag into slab itself.
This optimization is only available on 64bit architectures where free
bits are available for the flag.

Reviewed-by: Hao Li <hao.li@linux.dev>
Link: https://patch.msgid.link/20260727-b4-objext_split-v3-11-c29ef0f1f257@kernel.org
Reviewed-by: Harry Yoo <harry@kernel.org>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

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This commit is contained in:

Vlastimil Babka (SUSE) 2026-07-27 14:54:05 +02:00

parent c4ec6cb557

commit 7def2e8549

5 changed files with 61 additions and 8 deletions

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3

include/linux/slab.h

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3

mm/kfence/core.c

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31

mm/slab.h

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26

mm/slab_common.c

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6

mm/slub.c

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