linux-kernel - Re: [RFCv2][PATCH 0/5] mm: Batch page reclamation under shink_page

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Message-ID: <20130520215542.GC25536@cerebellum>
Date:	Mon, 20 May 2013 16:55:42 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mgorman@...e.de,
	tim.c.chen@...ux.intel.com
Subject: Re: [RFCv2][PATCH 0/5] mm: Batch page reclamation under
 shink_page_list

On Thu, May 16, 2013 at 01:34:27PM -0700, Dave Hansen wrote:
> These are an update of Tim Chen's earlier work:
> 
> 	http://lkml.kernel.org/r/1347293960.9977.70.camel@schen9-DESK
> 
> I broke the patches up a bit more, and tried to incorporate some
> changes based on some feedback from Mel and Andrew.
> 
> Changes for v2:
>  * use page_mapping() accessor instead of direct access
>    to page->mapping (could cause crashes when running in
>    to swap cache pages.
>  * group the batch function's introduction patch with
>    its first use
>  * rename a few functions as suggested by Mel
>  * Ran some single-threaded tests to look for regressions
>    caused by the batching.  If there is overhead, it is only
>    in the worst-case scenarios, and then only in hundreths of
>    a percent of CPU time.
> 
> If you're curious how effective the batching is, I have a quick
> and dirty patch to keep some stats:
> 
> 	https://www.sr71.net/~dave/intel/rmb-stats-only.patch
>

Didn't do any performance comparison but did a kernel build with 2 make threads
per core in a memory constrained situation w/ zswap add got an average batch
size of 6.6 pages with the batch being empty on ~10% of calls.

rmb call:   423464
rmb pages:   2790332
rmb empty:   41408

The WARN_ONCE only gave me one stack for the first empty batch and, for what
it's worth, it was from kswapd.

Tested-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>

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