From: Hao Li <hao.li@linux.dev>
To: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
Cc: Harry Yoo <harry@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Shakeel Butt <shakeel.butt@linux.dev>,
Alexander Potapenko <glider@google.com>,
Marco Elver <elver@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org
Subject: Re: [PATCH v2 12/13] mm/slab: add cache_ and slab_needs_objcg() helpers
Date: Mon, 27 Jul 2026 14:17:59 +0800 [thread overview]
Message-ID: <amb0jBAYvObMYBVv@fedora> (raw)
In-Reply-To: <df871664-09ea-4e83-bff0-bbd3ff9f3ccc@kernel.org>
On Fri, Jul 24, 2026 at 06:31:51PM +0200, Vlastimil Babka (SUSE) wrote:
> On 7/24/26 11:41, Hao Li wrote:
> > On Mon, Jul 20, 2026 at 04:16:26PM +0200, Vlastimil Babka (SUSE) wrote:
> >> 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 only
> >> is_kmalloc_normal() caches don't have the flag.
> >
> > it seems this could be "only type == KMALLOC_NORMAL caches don't have this
> > flag".
>
> I think not, because with SLUB_TINY,
Ah, right, I missed the SLUB_TINY case.
> a KMALLOC_NORMAL cache can have
> SLAB_RECLAIM_ACCOUNT flag and thus is not is_kmalloc_normal()
Just a minor detail though: under SLUB_TINY, SLAB_RECLAIM_ACCOUNT isn't used,
and new_kmalloc_cache() checks KMALLOC_RECLAIM != KMALLOC_NORMAL before setting
it. So is_kmalloc_normal() should still evaluate to true.
> and may need objcgs?
Agree. Under SLUB_TINY, we indeed need to set SLAB_MAY_ACCOUNT.
>
> Yep it's subtle :/
>
Yeah, it's pretty subtle. Since the full case matrix is tricky to summarize
accurately in one sentence, I think it might be cleaner to simply drop "only
is_kmalloc_normal() caches don't have the flag".
--
Thanks,
Hao
next prev parent reply other threads:[~2026-07-27 6:18 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 14:16 [PATCH v2 00/13] mm/slab, alloc_tag: reduce obj_ext memory waste Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 01/13] mm/slab: skip kfence objects in allocation profiling Vlastimil Babka (SUSE)
2026-07-21 5:43 ` Harry Yoo
2026-07-21 9:20 ` Vlastimil Babka (SUSE)
2026-07-21 15:41 ` Harry Yoo
2026-07-22 12:47 ` Hao Li
2026-07-24 15:58 ` Vlastimil Babka (SUSE)
2026-07-27 6:21 ` Hao Li
2026-07-20 14:16 ` [PATCH v2 02/13] mm/slub: skip handle_failed_objexts_alloc() with profiling disabled Vlastimil Babka (SUSE)
2026-07-21 5:51 ` Harry Yoo
2026-07-21 9:23 ` Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 03/13] mm/slab: remove objs_per_slab() Vlastimil Babka (SUSE)
2026-07-21 5:53 ` Harry Yoo
2026-07-20 14:16 ` [PATCH v2 04/13] mm: move struct slabobj_ext to mm/slab.h Vlastimil Babka (SUSE)
2026-07-21 5:55 ` Harry Yoo
2026-07-20 14:16 ` [PATCH v2 05/13] mm/slab: make slab_obj_ext() determine object index Vlastimil Babka (SUSE)
2026-07-21 6:02 ` Harry Yoo
2026-07-20 14:16 ` [PATCH v2 06/13] mm/slab: abstract slabobj_ext.objcg access Vlastimil Babka (SUSE)
[not found] ` <amH7ndu2TAd4ixKU@fedora>
2026-07-23 17:23 ` Suren Baghdasaryan
2026-07-20 14:16 ` [PATCH v2 07/13] mm/slab: abstract slabobj_ext.ref access Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 08/13] mm/slab: replace slab.stride with obj_exts_in_object Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 09/13] mm/slab: change struct slabobj_ext to a union Vlastimil Babka (SUSE)
2026-07-23 3:05 ` Hao Li
2026-07-23 6:27 ` Harry Yoo
[not found] ` <amHkbJsvOjcfUR3D@fedora>
2026-07-24 15:42 ` Vlastimil Babka (SUSE)
2026-07-27 5:41 ` Harry Yoo
2026-07-27 6:22 ` Hao Li
2026-07-20 14:16 ` [PATCH v2 10/13] mm/slab: introduce slab_obj_ext_has_codetag() Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 11/13] mm/slab: reduce slabobj_ext memory with allocation profiling disabled Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 12/13] mm/slab: add cache_ and slab_needs_objcg() helpers Vlastimil Babka (SUSE)
2026-07-24 9:41 ` Hao Li
2026-07-24 16:31 ` Vlastimil Babka (SUSE)
2026-07-27 6:17 ` Hao Li [this message]
2026-07-24 16:38 ` Vlastimil Babka (SUSE)
2026-07-20 14:16 ` [PATCH v2 13/13] mm/slab: stop allocating objcg pointers when unnecessary Vlastimil Babka (SUSE)
2026-07-24 9:57 ` Hao Li
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