linux-kernel - Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails

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Date:	Fri, 10 Sep 2010 16:17:46 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after
 direct reclaim allocation fails

On Thu, Sep 09, 2010 at 01:39:10PM +0100,  wrote:
> It has been pointed out that the fix potentially increases the number of
> IPIs sent. On larger machines, I worry that these delays could be severe
> and we'll see other problems down the line. Hence, I'd like to reduce
> the number of calls to drain_all_pages() without eliminating them
> entirely. I'm currently in the process of testing the following patch
> but can you try it as well please?
> 
> In particular, I am curious to see if the performance of fs_mark
> improves any and if the interrupt counts drop as a result of the patch.

The interrupt counts have definitely dropped - this is after
creating 200M inodes and then removing them all:

CAL:      11154 10596 11804 15366 10048 12916 13049 9864

That's in the same ballpark as a single 50M inode create run without
the patch.

Performance seems a bit lower, though (2-3% maybe less), and CPU
usage seems a bit higher (stays much closer to 800% than 700-750%
without the patch). Those are subjective observations from watching
graphs and counters, so take them with a grain of salt.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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