linux-kernel - Re: [PATCH 0/9] re-shrink 'struct page' when SLUB is on.

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Date:	Thu, 16 Jan 2014 10:44:24 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Dave Hansen <dave@...1.net>
cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/9] re-shrink 'struct page' when SLUB is on.

On Tue, 14 Jan 2014, Dave Hansen wrote:

> On 01/14/2014 12:07 PM, Christoph Lameter wrote:
> > One easy way to shrink struct page is to simply remove the feature. The
> > patchset looked a bit complicated and does many other things.
>
> Sure.  There's a clear path if you only care about 'struct page' size,
> or if you only care about making the slub fast path as fast as possible.
>  We've got three variables, though:
>
> 1. slub fast path speed

The fast path does use this_cpu_cmpxchg_double which is something
different from a cmpxchg_double and its not used on struct page.

> Arranged in three basic choices:
>
> 1. Big 'struct page', fast, medium complexity code
> 2. Small 'struct page', slow, lowest complexity

The numbers that I see seem to indicate that a big struct page means slow.

> The question is what we should do by _default_, and what we should be
> recommending for our customers via the distros.  Are you saying that you
> think we should completely rule out even having option 1 in mainline?

If option 1 is slower than option 2 then we do not need it.

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