Re: [lkp] [+5395 bytes kernel size regression] [i386-tinyconfig] [b7c8731082] Deprecating and removing SLOB

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Nov 11, 2022 at 08:49:57PM +0800, kernel test robot wrote:
> FYI, we noticed a +5395 bytes kernel size regression due to commit:
> 
> commit: b7c873108294f0fd19c7e4d6b038a05375b3cd33 (Deprecating and removing SLOB)
> url: https://github.com/intel-lab-lkp/linux/commits/Vlastimil-Babka/mm-slob-rename-CONFIG_SLOB-to-CONFIG_SLOB_DEPRECATED/20221111-183529
> base: https://git.kernel.org/cgit/linux/kernel/git/akpm/mm.git mm-everything
> patch subject: [PATCH] mm, slob: rename CONFIG_SLOB to CONFIG_SLOB_DEPRECATED
> 
> 
> Details as below (size data is obtained by `nm --size-sort vmlinux`):
> 
> e1e3de44: Merge branch 'mm-nonmm-unstable' into mm-everything
> b7c87310: Deprecating and removing SLOB

This patch has the net effect of switching tiny over from SLOB to SLUB,
which causes a 5k+ size regression.

I *absolutely* appreciate the value of removing this much code, and I'm
not going to propose keeping SLOB for the sole reason of being 5k
smaller; it's not worth keeping a whole allocator for that. I also
wouldn't be surprised if we get *some* of that back by simplifications
this change enables in the rest of the kernel.

But I'm wondering if there might be any low-hanging fruit that could
slim down SLUB to the tune of 5k or so, that has been previously ignored
because SLOB served that use case? For instance, largely self-contained
bits of SLUB functionality that could be omitted on the tiniest of
systems?

- Josh Triplett