From: Andrew Morton <akpm@linux-foundation.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>, Minchan Kim <minchan@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Andrea Arcangeli <aarcange@redhat.com>,
David Rientjes <rientjes@google.com>,
Michal Hocko <mhocko@suse.cz>,
Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Matthew Wilcox <willy@linux.intel.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andi Kleen <ak@linux.intel.com>,
linux-mm@kvack.org, linux-kernel <linux-kernel@vger.kernel.org>,
Alex Shi <alex.shi@intel.com>,
Fengguang Wu <fengguang.wu@intel.com>
Subject: Re: [PATCH 0/3 v2] mm: Batch page reclamation under shink_page_list
Date: Wed, 12 Sep 2012 12:27:58 -0700 [thread overview]
Message-ID: <20120912122758.ad15e10f.akpm@linux-foundation.org> (raw)
In-Reply-To: <1347293960.9977.70.camel@schen9-DESK>
On Mon, 10 Sep 2012 09:19:20 -0700
Tim Chen <tim.c.chen@linux.intel.com> wrote:
> This is the second version of the patch series. Thanks to Matthew Wilcox
> for many valuable suggestions on improving the patches.
>
> To do page reclamation in shrink_page_list function, there are two
> locks taken on a page by page basis. One is the tree lock protecting
> the radix tree of the page mapping and the other is the
> mapping->i_mmap_mutex protecting the mapped
> pages. I try to batch the operations on pages sharing the same lock
> to reduce lock contentions. The first patch batch the operations protected by
> tree lock while the second and third patch batch the operations protected by
> the i_mmap_mutex.
>
> I managed to get 14% throughput improvement when with a workload putting
> heavy pressure of page cache by reading many large mmaped files
> simultaneously on a 8 socket Westmere server.
That sounds good, although more details on the performance changes
would be appreciated - after all, that's the entire point of the
patchset.
And we shouldn't only test for improvements - we should also test for
degradation. What workloads might be harmed by this change? I'd suggest
- a single process which opens N files and reads one page from each
one, then repeats. So there are no contiguous LRU pages which share
the same ->mapping. Get some page reclaim happening, measure the
impact.
- The batching means that we now do multiple passes over pageframes
where we used to do things in a single pass. Walking all those new
page lists will be expensive if they are lengthy enough to cause L1
cache evictions.
What would be a test for this? A simple, single-threaded walk
through a file, I guess?
Mel's review comments were useful, thanks.
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next prev parent reply other threads:[~2012-09-12 19:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-10 16:19 [PATCH 0/3 v2] mm: Batch page reclamation under shink_page_list Tim Chen
2012-09-11 5:36 ` Minchan Kim
2012-09-13 16:08 ` Tim Chen
2012-09-12 19:27 ` Andrew Morton [this message]
2012-09-12 23:44 ` Tim Chen
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