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

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Message-Id: <1179164453.2942.26.camel@lappy>
Date:	Mon, 14 May 2007 19:40:52 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <clameter@....com>
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 Mon, 2007-05-14 at 09:29 -0700, Christoph Lameter wrote:
> On Mon, 14 May 2007, Matt Mackall wrote:
> 
> > privileged thread                      unprivileged greedy process
> > kmem_cache_alloc(...)
> >    adds new slab page from lowmem pool
> 
> Yes but it returns an object for the privileged thread. Is that not 
> enough?

No, because we reserved memory for n objects, and like matt illustrates
most of those that will be eaten by the greedy process.

We could reserve 1 page per object but that rather bloats the reserve.

> > do_io()
> >                                        kmem_cache_alloc(...)
> >                                        kmem_cache_alloc(...)
> >                                        kmem_cache_alloc(...)
> >                                        kmem_cache_alloc(...)
> >                                        kmem_cache_alloc(...)
> >                                        ...
> >                                           eats it all
> > kmem_cache_alloc(...) -> ENOMEM
> >    who ate my donuts?!
> > 
> > But I think this solution is somehow overkill. If we only care about
> > this issue in the OOM avoidance case, then our rank reduces to a
> > boolean.

I tried to slim it down to a two state affair; but last time I tried
performance runs that actually slowed it down some.

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