linux-kernel - Re: [GIT PULL] scheduler fixes

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Date:	Thu, 28 May 2009 15:06:40 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>, Jeff Garzik <jgarzik@...ox.com>,
	Alexander Viro <viro@....linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	cl@...ux-foundation.org, mpm@...enic.com
Subject: Re: [GIT PULL] scheduler fixes

On Tue, 2009-05-26 at 09:38 +0200, Nick Piggin wrote:
> On Mon, May 25, 2009 at 09:39:08PM +0300, Pekka Enberg wrote:
> > Linus Torvalds wrote:
> > >And vfs_caches_init_early() is actually doing some rather strange things, 
> > >like doing a "alloc_large_system_hash()" but not unconditionally: it does 
> > >it in the "late" initialization too, if not done early. inode_init_early 
> > >does soemthing very similar (ie a _conditional_ early init).
> > >
> > >So none of this seems to really get a huge advantage from the early init. 
> > >There seems to be some subtle NUMA issues, but do we really want that? I 
> > >get the feeling that nobody ever wanted to do it early, and then the NUMA 
> > >people said "I don't wnt to do this early, but I don't want to touch the 
> > >non-NUMA case, so I'll do it early for non-numa, and late for numa".
> > 
> > SLUB does sysfs setup in kmem_cache_init() and if I saw some oopses if I 
> > don't call vfs_caches_init_early() first. I didn't look too closely, though.
> 
> Did you also test the NUMA/hashdist case? vfs_caches_init_early doesn't
> do much in that case.

No, I tested UMA only.

On Tue, 2009-05-26 at 09:38 +0200, Nick Piggin wrote:
> I would say it is much more robust to do sysfs setup later if we move
> the slab setup so early. Probably it is just quite lucky not to explode
> in the !numa case because the vfs needs quite a bit of setting up...

That should not be an issue. SLUB already defers sysfs registration
until slab_sysfs_init() initcall has been run. So my patches have zero
change in how SLUB interracts with sysfs, actually.

			Pekka

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