linux-kernel - Re: Linux 2.6.29

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Message-ID: <49CACD0B.4060901@redhat.com>
Date:	Wed, 25 Mar 2009 20:32:11 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Bron Gondwana <brong@...tmail.fm>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

Bron Gondwana wrote:
> On Wed, Mar 25, 2009 at 04:23:08PM -0700, Linus Torvalds wrote:
>   
>> On Wed, 25 Mar 2009, Theodore Tso wrote:
>>     
>>>> The problem being that unlike the ratio, there's no sane default value 
>>>> that you can at least argue is not _entirely_ pointless.
>>>>         
>>> Well, if the maximum time that someone wants to wait for an fsync() to
>>> return is one second, and the RAID array can write 100MB/sec
>>>       
>> How are you going to tell the kernel that the RAID array can write 
>> 100MB/s?
>>
>> The kernel has no idea.
>>     
>
> Not at boot up, but after it's been using the RAID array for a little
> while it could...
>
> Bron (... imagining a tunable "max_fsync_wait_target_centisecs = 100" 
>       which caused the kernel to notice how long flushes were taking
>       and tune its buffer sizes to be approximately right over time )
>   
This tuning logic is the core of what Josef Bacik did for the 
transaction batching code for ext4....

ric

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