linux-kernel - Re: [PATCH 0/5] make slab gfp fair

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Message-ID: <Pine.LNX.4.64.0705161320020.11018@schroedinger.engr.sgi.com>
Date:	Wed, 16 May 2007 13:27:00 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Thomas Graf <tgraf@...g.ch>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/5] make slab gfp fair

On Wed, 16 May 2007, Peter Zijlstra wrote:

> > So its no use on NUMA?
> 
> It is, its just that we're swapping very heavily at that point, a
> bouncing cache-line will not significantly slow down the box compared to
> waiting for block IO, will it?

How does all of this interact with

1. cpusets

2. dma allocations and highmem?

3. Containers?

> > The problem here is that you may spinlock and take out the slab for one 
> > cpu but then (AFAICT) other cpus can still not get their high priority 
> > allocs satisfied. Some comments follow.
> 
> All cpus are redirected to ->reserve_slab when the regular allocations
> start to fail.

And the reserve slab is refilled from page allocator reserves if needed?

> > But this is only working if we are using the slab after
> > explicitly flushing the cpuslabs. Otherwise the slab may be full and we
> > get to alloc_slab.
> 
> /me fails to parse.

s->cpu[cpu] is only NULL if the cpu slab was flushed. This is a pretty 
rare case likely not worth checking.

 
> > Remove the above two lines (they are wrong regardless) and simply make 
> > this the cpu slab.
> 
> It need not be the same node; the reserve_slab is node agnostic.
> So here the free page watermarks are good again, and we can forget all
> about the ->reserve_slab. We just push it on the free/partial lists and
> forget about it.
> 
> But like you said above: unfreeze_slab() should be good, since I don't
> use the lockless_freelist.

You could completely bypass the regular allocation functions and do

object = s->reserve_slab->freelist;
s->reserve_slab->freelist = object[s->reserve_slab->offset];

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