linux-kernel - Re: [patch] SLQB slab allocator (try 2)

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Date:	Thu, 19 Feb 2009 09:05:10 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	kosaki.motohiro@...fujitsu.com,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mel@....ul.ie>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Nick Piggin <npiggin@...e.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lin Ming <ming.m.lin@...el.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Subject: Re: [patch] SLQB slab allocator (try 2)

Hi Pekka,

> Hi!
> 
> On Wed, 2009-02-18 at 09:48 +0900, KOSAKI Motohiro wrote:
> > I think 2 * PAGE_SIZE is best and the patch description is needed change.
> > it's because almost architecture use two pages for stack and current page
> > allocator don't have delayed consolidation mechanism for order-1 page.
> 
> Do you mean alloc_thread_info()? Not all architectures use kmalloc() to
> implement it so I'm not sure if that's relevant for this patch.
> 
> On Wed, 2009-02-18 at 09:48 +0900, KOSAKI Motohiro wrote:
> > In addition, if pekka patch (SLAB_LIMIT = 8K) run on ia64, 16K allocation 
> > always fallback to page allocator and using 64K (4 times memory consumption!).
> 
> Yes, correct, but SLUB does that already by passing all allocations over
> 4K to the page allocator.

hmhm
OK. my mail was pointless.

but why? In my understanding, slab framework mainly exist for efficient
sub-page allocation.
the fallbacking of 4K allocation in 64K page-sized architecture seems
inefficient.


> I'm not totally against 2 * PAGE_SIZE but I just worry that as SLUB
> performance will be bound to architecture page size, we will see skewed
> results in performance tests without realizing it. That's why I'm in
> favor of a fixed size that's unified across architectures.

fair point.



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