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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: [patch] SLQB slab allocator (try 2)
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Date: Thu, 19 Feb 2009 09:05:10 +0900 (JST)
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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.