linux-kernel - Re: [PATCH] procfs: provide slub's /proc/slabinfo

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Date:	Thu, 3 Jan 2008 09:52:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Hugh Dickins <hugh@...itas.com>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] procfs: provide slub's /proc/slabinfo

* Matt Mackall <mpm@...enic.com> wrote:

> > Which means that SLOB could also trivially implement the same thing, 
> > with no new #ifdef'fery or other crud.
> 
> Except SLOB's emulation of slabs is so thin, it doesn't have the 
> relevant information. We have a very small struct kmem_cache, which I 
> suppose could contain a counter. But we don't have anything like the 
> kmalloc slabs, so you'd only be getting half the picture anyway. The 
> output of slabtop would simply be misleading because there are no 
> underlying "slabs" in the first place.

i think SLOB/embedded is sufficiently special that a "no /proc/slabinfo" 
restriction is perfectly supportable. (for instance it's only selectable 
if CONFIG_EMBEDDED=y) If a SLOB user has any memory allocation problems 
it's worth going to the bigger allocators anyway, to get all the 
debugging goodies.

btw., do you think it would be worth/possible to have build mode for 
SLUB that is acceptably close to the memory efficiency of SLOB? (and 
hence work towards unifying all the 3 allocators into SLUB in essence)

right now we are far away from it - SLUB has an order of magnitude 
larger .o than SLOB, even on UP. I'm wondering why that is so - SLUB's 
data structures _are_ quite compact and could in theory be used in a 
SLOB-alike way. Perhaps one problem is that much of SLUB's debugging 
code is always built in?

	Ingo
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