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

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Date: Wed, 31 Jan 2024 17:20:27 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Cc: 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: Do we still need SLAB_MEM_SPREAD (and possibly others)?

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.

-- Steve