linux-kernel - Re: Mainline kernel OLTP performance update

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Message-Id: <1232724691.6094.86.camel@penberg-laptop>
Date:	Fri, 23 Jan 2009 17:31:31 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, Stephen Rothwell <sfr@...b.auug.org.au>,
	matthew.r.wilcox@...el.com, chinang.ma@...el.com,
	linux-kernel@...r.kernel.org, sharad.c.tripathi@...el.com,
	arjan@...ux.intel.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@...gic.com,
	anirban.chakraborty@...gic.com, Ingo Molnar <mingo@...e.hu>
Subject: Re: Mainline kernel OLTP performance update

On Fri, 2009-01-23 at 10:22 -0500, Christoph Lameter wrote:
> On Fri, 23 Jan 2009, Pekka Enberg wrote:
> 
> > Looking at __slab_free(), unless page->inuse is constantly zero and we
> > discard the slab, it really is just cache effects (10% sounds like a
> > lot, though!). AFAICT, the only way to optimize that is with Christoph's
> > unfinished pointer freelists patches or with a remote free list like in
> > SLQB.
> 
> No there is another way. Increase the allocator order to 3 for the
> kmalloc-8192 slab then multiple 8k blocks can be allocated from one of the
> larger chunks of data gotten from the page allocator. That will allow slub
> to do fast allocs.

I wonder why that doesn't happen already, actually. The slub_max_order
know is capped to PAGE_ALLOC_COSTLY_ORDER ("3") by default and obviously
order 3 should be as good fit as order 2 so 'fraction' can't be too high
either. Hmm.

		Pekka

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