linux-kernel - Re: Mainline kernel OLTP performance update

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Date:	Thu, 15 Jan 2009 18:24:36 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Matthew Wilcox <matthew@....cx>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	chinang.ma@...el.com, linux-kernel@...r.kernel.org,
	sharad.c.tripathi@...el.com, arjan@...ux.intel.com,
	andi.kleen@...el.com, suresh.b.siddha@...el.com,
	harita.chilukuri@...el.com, douglas.w.styner@...el.com,
	peter.xihong.wang@...el.com, hubert.nueckel@...el.com,
	chris.mason@...cle.com, srostedt@...hat.com,
	linux-scsi@...r.kernel.org,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	Anirban Chakraborty <anirban.chakraborty@...gic.com>
Subject: Re: Mainline kernel OLTP performance update

On Thursday 15 January 2009 13:04:31 Andrew Morton wrote:
> On Wed, 14 Jan 2009 18:21:47 -0700 Matthew Wilcox <matthew@....cx> wrote:

> > SLUB would have had a huge negative effect if we were using it -- on the
> > order of 7% iirc.  SLQB is at least performance-neutral with SLAB.
>
> We really need to unblock that problem somehow.  I assume that
> enterprise distros are shipping slab?

SLES11 will ship with SLAB, FWIW. As I said in the SLQB thread, this was
not due to my input. But I think it was probably the right choice to make
in that situation.

The biggest problem with SLAB for SGI I think is alien caches bloating the
kmem cache footprint to many GB each on their huge systems, but SLAB has a
parameter to turn off alien caches anyway so I think that is a reasonable
workaround.

Given the OLTP regression, and also I'd hate to have to deal with even
more reports of people's order-N allocations failing... basically with the
regression potential there, I don't think there was a compelling case
found to use SLUB (ie. where does it actually help?).

I'm going to propose to try to unblock the problem by asking to merge SLQB
with a plan to end up picking just one general allocator (and SLOB).

Given that SLAB and SLUB are fairly mature, I wonder what you'd think of
taking SLQB into -mm and making it the default there for a while, to see
if anybody reports a problem?

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