linux-kernel - Re: [PATCH 0/3] VM throttling: avoid blocking occasional writers

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Message-ID: <45FD53DB.5000207@tmr.com>
Date:	Sun, 18 Mar 2007 09:59:39 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>,
	linux-kernel@...r.kernel.org, yumiko.sugita.yf@...achi.com,
	masami.hiramatsu.pt@...achi.com, hidehiro.kawai.ez@...achi.com,
	yuji.kakutani.uw@...achi.com, soshima@...hat.com, haoki@...hat.com,
	kamezawa.hiroyu@...fujitsu.com, nikita@...sterfs.com,
	leroy.vanlogchem@...elft.nl
Subject: Re: [PATCH 0/3] VM throttling: avoid blocking occasional writers

Andrew Morton wrote:
>> On Wed, 14 Mar 2007 21:42:46 +0900 Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com> wrote:
>>
>> ...
>>
>>
>> -Solution:
>>
>> I consider that all of the dirty pages for the disk have been written
>> back and that the disk is clean if a process cannot write 'write_chunk'
>> pages in balance_dirty_pages().
>>
>> To avoid using up the free memory with dirty pages by passing blocking,
>> this patchset adds a new threshold named vm.dirty_limit_ratio to sysctl.
>>
>> It modifies balance_dirty_pages() not to block when the amount of
>> Dirty+Writeback is less than vm.dirty_limit_ratio percent of the memory.
>> In the other cases, writers are throttled as current Linux does.
>>
>>
>> In this patchset, vm.dirty_limit_ratio, instead of vm.dirty_ratio, is
>> used as the clamping level of Dirty+Writeback. And, vm.dirty_ratio is
>> used as the level at which a writers will itself start writeback of the
>> dirty pages.
> 
> Might be a reasonable solution - let's see what Peter comes up with too.
> 
> Comments on the patch:
> 
> - Please don't VM_DIRTY_LIMIT_RATIO: just use CTL_UNNUMBERED and leave
>   sysctl.h alone.
> 
> - The 40% default is already too high.  Let's set this new upper limit to
>   40% and decrease he non-blocking ratio.
> 
> - Please update the procfs documentation in ./Docmentation/
> 
> - I wonder if dirty_limit_ratio is the best name we could choose. 
>   vm_dirty_blocking_ratio, perhaps?  Dunno.
> 
I don't like it, but I dislike it less than "dirty_limit_ratio" I guess. 
It would probably break things to change it now, including my 
sysctl.conf on a number of systems :-(

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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