Do we still need SLAB_MEM_SPREAD (and possibly others)?

Steven Rostedt
2024-01-31T22:20:22Z

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