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Date: Thu, 30 Jul 2009 12:55:44 -0700
Message-ID: <33307c790907301255j136e003dtac0e4ba2032e890e@mail.gmail.com>
Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout
From: Martin Bligh <mbligh@google.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       Michael Rubin <mrubin@google.com>,
       "sandeen@redhat.com" <sandeen@redhat.com>,
       Michael Davidson <md@google.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <peterz@infradead.org>
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> Note that this is a simple fix that may have suboptimal write performance.
> Here is an old reasoning:
>
> ? ? ? ?http://lkml.org/lkml/2009/3/28/235

The other thing I've been experimenting with is to disable the per-page
check in write_cache_pages, ie:

                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
                                wb_stats_inc(WB_STATS_WCP_SECTION_CONG);
                                wbc->encountered_congestion = 1;
                                /* done = 1; */

This treats the congestion limits as soft, but encourages us to write
back in larger, more efficient chunks. If that's not going to scare
people unduly, I can submit that as well.
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