linux-kernel - Re: [patch 09/10] Remove the SLOB allocator for 2.6.23

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Message-ID: <20070708075119.GA16631@elte.hu>
Date:	Sun, 8 Jul 2007 09:51:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
	suresh.b.siddha@...el.com, corey.d.gough@...el.com,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, Matt Mackall <mpm@...enic.com>
Subject: Re: [patch 09/10] Remove the SLOB allocator for 2.6.23


(added Matt to the Cc: list)

* Christoph Lameter <clameter@....com> wrote:

> Maintenance of slab allocators becomes a problem as new features for 
> allocators are developed. The SLOB allocator in particular has been 
> lagging behind in many ways in the past:
> 
> - Had no support for SLAB_DESTROY_BY_RCU for years (but no one 
>   noticed)
> 
> - Still has no support for slab reclaim counters. This may currently 
>   not be necessary if one would restrict the supported configurations 
>   for functionality relying on these. But even that has not been done.
> 
> The only current advantage over SLUB in terms of memory savings is 
> through SLOBs kmalloc layout that is not power of two based like SLAB 
> and SLUB which allows to eliminate some memory waste.
> 
> Through that SLOB has still a slight memory advantage over SLUB of 
> ~350k in for a standard server configuration. It is likely that the 
> savings are is smaller for real embedded configurations that have less 
> functionality.

actually, one real advantage of the SLOB is that it is a minimal, really 
simple allocator. Its text and data size is so small as well.

here's the size comparison:

   text    data     bss     dec     hex filename
  10788     837      16   11641    2d79 mm/slab.o
   6205    4207     124   10536    2928 mm/slub.o
   1640      44       4    1688     698 mm/slob.o

slab/slub have roughly the same footprint, but slob is 10% of that size. 
Would be a waste to throw this away.

A year ago the -rt kernel defaulted to the SLOB for a few releases, and 
barring some initial scalability issues (which were solved in -rt) it 
worked pretty well on generic PCs, so i dont buy the 'it doesnt work' 
argument either.

	Ingo
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