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Subject: Re: [patch] SLQB slab allocator (try 2)
From: Pekka Enberg <penberg@cs.helsinki.fi>
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Date: Wed, 18 Feb 2009 10:09:29 +0200
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To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <nickpiggin@yahoo.com.au>, Nick Piggin <npiggin@suse.de>, Linux Memory Management List <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Lin Ming <ming.m.lin@intel.com>, "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
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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.

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.

			Pekka

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