linux-kernel - Re: [PATCH 61 of 66] use compaction for GFP

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Date:	Tue,  9 Nov 2010 19:27:37 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>, bpicco@...hat.com,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Chris Mason <chris.mason@...cle.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 61 of 66] use compaction for GFP_ATOMIC order > 0

> From: Andrea Arcangeli <aarcange@...hat.com>
> 
> This takes advantage of memory compaction to properly generate pages of order >
> 0 if regular page reclaim fails and priority level becomes more severe and we
> don't reach the proper watermarks.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>

First, I don't think this patch is related to GFP_ATOMIC. So, I think the 
patch title is a bit misleading.

Second, this patch has two changes. 1) remove PAGE_ALLOC_COSTLY_ORDER 
threshold 2) implement background compaction. please separate them.

Third, This patch makes a lot of PFN order page scan and churn LRU
aggressively. I'm not sure this aggressive lru shuffling is safe and
works effective. I hope you provide some demonstration and/or show 
benchmark result.

Thanks.



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