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Subject: Re: [PATCH 0/5] make slab gfp fair
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Christoph Lameter <clameter@sgi.com>
Cc: Matt Mackall <mpm@selenic.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, Thomas Graf <tgraf@suug.ch>,
       David Miller <davem@davemloft.net>,
       Andrew Morton <akpm@linux-foundation.org>,
       Daniel Phillips <phillips@google.com>,
       Pekka Enberg <penberg@cs.helsinki.fi>
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Date: Mon, 14 May 2007 19:40:52 +0200
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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.