linux-kernel - Re: [PATCH 04/10] mm: slub: add knowledge of reserve pages

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Date:	Mon, 20 Aug 2007 12:26:09 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Matt Mackall <mpm@...enic.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Steve Dickson <SteveD@...hat.com>
Subject: Re: [PATCH 04/10] mm: slub: add knowledge of reserve pages

On Mon, 20 Aug 2007, Pekka Enberg wrote:

> Hi Peter,
> 
> On Mon, 2007-08-20 at 12:12 +0300, Pekka J Enberg wrote:
> > > Any reason why the callers that are actually interested in this don't do
> > > page->reserve on their own?
> 
> On 8/20/07, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > because new_slab() destroys the content?
> 
> Right. So maybe we could move the initialization parts of new_slab()
> to __new_slab() so that the callers that are actually interested in
> 'reserve' could do allocate_slab(), store page->reserve and do rest of
> the initialization with it?

I am still not convinced about this approach and there seems to be 
agreement that this is not working on large NUMA. So #ifdef it out? 
!CONFIG_NUMA? Some more general approach that does not rely on a single 
slab being a reserve?

The object is to check the alloc flags when having allocated a reserve 
slab right? Adding another flag SlabReserve and keying off on that one may 
be the easiest solution.

I have pending patches here that add per cpu structures. Those will make 
that job easier.

> As for the __GFP_WAIT handling, I *think* we can move the interrupt
> enable/disable to allocate_slab()... Christoph?

The reason the enable/disable is in new_slab is to minimize interrupt 
holdoff time. If we move it to allocate slab then the slab preparation is 
done with interrupts disabled.
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