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Date: Wed, 21 Mar 2012 13:20:11 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: Eric Dumazet <eric.dumazet@gmail.com>
cc: Tejun Heo <tj@kernel.org>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: Patch workqueue: create new slab cache instead of hacking
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On Wed, 21 Mar 2012, Eric Dumazet wrote:

> On Wed, 2012-03-21 at 12:54 -0500, Christoph Lameter wrote:
> > On Wed, 21 Mar 2012, Eric Dumazet wrote:
> >
> > > On Wed, 2012-03-21 at 10:03 -0500, Christoph Lameter wrote:
> > > > On Wed, 21 Mar 2012, Eric Dumazet wrote:
> > > >
> > > > > Creating a dedicated cache for few objects ? Thats a lot of overhead, at
> > > > > least for SLAB (no merges of caches)
> > > >
> > > > Its some overhead for SLAB (a lot is what? If you tune down the per cpu
> > > > caches it should be a couple of pages) but its none for SLUB.
> > >
> > > SLAB overhead per cache is O(CPUS * nr_node_ids)  (unless alien caches
> > > are disabled)
> >
> > nr_node_ids==2 in the standard case these days. Alien caches are minimal.
>
>
> Thats not true. Some machines use lots of nodes (fake nodes) for various
> reasons.

Which is not a typical use case.

> And they cant disable alien caches for performance reasons.

Ok then lets genericize the slub merge in some form so that it works for
all slab allocators.