Received-SPF: pass (google.com: domain of linux-kernel+bounces-47257-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240131172027.10f64405@gandalf.local.home>
In-Reply-To: <20240131172027.10f64405@gandalf.local.home>
From: Yosry Ahmed <yosryahmed@google.com>
Date: Wed, 31 Jan 2024 14:25:49 -0800
Message-ID: <CAJD7tkYCrFAXLey-WK8k1Nkt4SoUQ00GWNjU43HJgaLqycBm7Q@mail.gmail.com>
Subject: Re: Do we still need SLAB_MEM_SPREAD (and possibly others)?
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, 
	Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, 
	Vlastimil Babka <vbabka@suse.cz>, Kees Cook <keescook@chromium.org>, Christoph Lameter <cl@linux.com>, 
	David Rientjes <rientjes@google.com>, Hyeonggon Yoo <42.hyeyoo@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Jan 31, 2024 at 2:20=E2=80=AFPM Steven Rostedt <rostedt@goodmis.org=
> wrote:
>
> I was looking into moving eventfs_inode into a slab, and after cutting an=
d
> pasting the tracefs allocator:
>
>         tracefs_inode_cachep =3D kmem_cache_create("tracefs_inode_cache",
>                                                  sizeof(struct tracefs_in=
ode),
>                                                  0, (SLAB_RECLAIM_ACCOUNT=
|
>                                                      SLAB_MEM_SPREAD|
>                                                      SLAB_ACCOUNT),
>                                                  init_once);
>
> I figured I should know what those slab flags mean. I also looked at what
> others in fs use for their slabs. The above is rather common (which I
> probably just copied from another file system), but I wanted to know what
> they are for.
>
> When I got to SLAB_MEM_SPREAD, I found that it's a common flag and there'=
s
> a lot of caches that just set that and nothing else.
>
> But I couldn't find how it was used.
>
> Then I found this commit:
>
>  16a1d968358a ("mm/slab: remove mm/slab.c and slab_def.h")
>
> Which I think removed the only use case of SLAB_MEM_SPREAD.
>
>  $ git grep SLAB_MEM_SPREAD mm
> mm/slab.h:                            SLAB_MEM_SPREAD | \
>
> That's all I find in the mm directory.
>
> Is it obsolete now? Can we delete it? Maybe there's other SLAB_* flags th=
at
> are no longer used. I don't know, I haven't audited them.

Perhaps cpuset_do_slab_mem_spread() as well.