linux-kernel - Re: [PATCH 0/9] Reduce system disruption due to kswapd V4

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Date:	Sat, 18 May 2013 23:15:34 +0200
From:	Zlatko Calusic <zcalusic@...sync.net>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>
CC:	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>, Michal Hocko <mhocko@...e.cz>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/9] Reduce system disruption due to kswapd V4

On 15.05.2013 22:37, Andrew Morton wrote:
>>
>>                              3.10.0-rc1  3.10.0-rc1
>>                                 vanilla lessdisrupt-v4
>> Page Ins                       1234608      101892
>> Page Outs                     12446272    11810468
>> Swap Ins                        283406           0
>> Swap Outs                       698469       27882
>> Direct pages scanned                 0      136480
>> Kswapd pages scanned           6266537     5369364
>> Kswapd pages reclaimed         1088989      930832
>> Direct pages reclaimed               0      120901
>> Kswapd efficiency                  17%         17%
>> Kswapd velocity               5398.371    4635.115
>> Direct efficiency                 100%         88%
>> Direct velocity                  0.000     117.817
>> Percentage direct scans             0%          2%
>> Page writes by reclaim         1655843     4009929
>> Page writes file                957374     3982047
>> Page writes anon                698469       27882
>> Page reclaim immediate            5245        1745
>> Page rescued immediate               0           0
>> Slabs scanned                    33664       25216
>> Direct inode steals                  0           0
>> Kswapd inode steals              19409         778
>
> The reduction in inode steals might be a significant thing?
> prune_icache_sb() does invalidate_mapping_pages() and can have the bad
> habit of shooting down a vast number of pagecache pages (for a large
> file) in a single hit.  Did this workload use large (and clean) files?
> Did you run any test which would expose this effect?
>

I did not run specific tests, but I believe I observed exactly this 
issue on the real workload, where even at a moderate load sudden frees 
of pagecache happen quite often. I've attached a small graph where it 
can be easily seen. The snapshot was taken while the server was running 
an unpatched Linus kernel. After the Mel's patch series is applied, I 
can't see anything similar. So it seems that this issue is completely 
gone, Mel's done a wonderful job.

And BTW, V4 continues to be rock stable, running here on many different 
machines, so I look forward seeing this code merged in 3.11.
-- 
Zlatko

Download attachment "memory-hourly.png" of type "image/png" (11951 bytes)