linux-kernel - Re: Do we still need SLAB_MEM_SPREAD (and possibly others)?

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Message-ID: <CAJD7tkYCrFAXLey-WK8k1Nkt4SoUQ00GWNjU43HJgaLqycBm7Q@mail.gmail.com>
Date: Wed, 31 Jan 2024 14:25:49 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Vlastimil Babka <vbabka@...e.cz>, Kees Cook <keescook@...omium.org>, Christoph Lameter <cl@...ux.com>, 
	David Rientjes <rientjes@...gle.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: Do we still need SLAB_MEM_SPREAD (and possibly others)?

On Wed, Jan 31, 2024 at 2:20 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> I was looking into moving eventfs_inode into a slab, and after cutting and
> pasting the tracefs allocator:
>
>         tracefs_inode_cachep = kmem_cache_create("tracefs_inode_cache",
>                                                  sizeof(struct tracefs_inode),
>                                                  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 that
> are no longer used. I don't know, I haven't audited them.

Perhaps cpuset_do_slab_mem_spread() as well.