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Date: Mon, 12 Apr 2010 09:18:56 +0300
Message-ID: <r2j84144f021004112318v78f28c3ds46531d1233966a20@mail.gmail.com>
Subject: Re: [PATCH 00 of 41] Transparent Hugepage Support #17
From: Pekka Enberg <penberg@cs.helsinki.fi>
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Sender: owner-linux-mm@kvack.org
To: Nick Piggin <npiggin@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>, Avi Kivity <avi@redhat.com>, Mike Galbraith <efault@gmx.de>, Jason Garrett-Glaser <darkshikari@gmail.com>, Andrea Arcangeli <aarcange@redhat.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Mike Travis <travis@sgi.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, Arnd Bergmann <arnd@arndb.de>, "Michael S. Tsirkin" <mst@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Johannes Weiner <hannes@cmpxchg.org>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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On Mon, Apr 12, 2010 at 9:09 AM, Nick Piggin <npiggin@suse.de> wrote:
>> I think Andrea and Mel and you demonstrated that while defrag is futile in
>> theory (we can always fill up all of RAM with dentries and there's no 2MB
>> allocation possible), it seems rather usable in practice.
>
> One problem is that you need to keep a lot more memory free in order
> for it to be reasonably effective. Another thing is that the problem
> of fragmentation breakdown is not just a one-shot event that fills
> memory with pinned objects. It is a slow degredation.
>
> Especially when you use something like SLUB as the memory allocator
> which requires higher order allocations for objects which are pinned
> in kernel memory.

I guess we'd need to merge the SLUB defragmentation patches to fix that?

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