From: Nikita Danilov <nikita@clusterfs.com>
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Date: Sat, 24 Feb 2007 16:15:26 +0300
To: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, miklos@szeredi.hu,
       yumiko.sugita.yf@hitachi.com, masami.hiramatsu.pt@hitachi.com,
       hidehiro.kawai.ez@hitachi.com, yuji.kakutani.uw@hitachi.com,
       soshima@redhat.com, haoki@redhat.com
Subject: Re: [RFC][PATCH 0/3] VM throttling: avoid blocking occasional writers
Newsgroups: gmane.linux.kernel
In-Reply-To: <45DED819.9040404@hitachi.com>
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Tomoki Sekiyama writes:
 > Hi,

Hello,

 > 

[...]

 > 
 > While Dirty+Writeback pages get more than 40% of memory, process-B is
 > blocked in balance_dirty_pages() until writeback of some (`write_chunk',
 > typically = 1536) dirty pages on disk-b is started.

May be the simpler solution is to use separate variables to control
ratelimit and write chunk?

writeback_set_ratelimit() adjusts ratelimit_pages to avoid too frequent
calls to balance_dirty_pages(), but once we are inside of
writeback_inodes(), there is no need to write especially many pages in
one go: overhead of any additional looping is negligible, when compared
with the cost of writing.

Speaking of which, now that expensive get_writeback_state() is gone from
page-writeback.c why do we need adjustable ratelimiting at all? It looks
like writeback_set_ratelimit() can be dropped, and fixed ratelimit used
instead.

Nikita.

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