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Date: Fri, 27 Mar 2009 15:10:56 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Jan Kara <jack@suse.cz>
cc: Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
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Subject: Re: ext3 IO latency measurements (was: Linux 2.6.29)
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On Fri, 27 Mar 2009, Jan Kara wrote:
>
>   Doable but not fairly simple ;) Firstly you have to restart a transaction
> when you've used up all the credits you originally started with (easy),
> secondly ext3 uses lock order PageLock -> "transaction start" which is
> unusable for the scheme you suggest. So we'd have to revert that - which
> needs larger audit of our locking scheme and that's probably the reason
> why noone has done it yet.

It's also not clear that ext3 can really do much better than the regular 
generic_writepages() logic. I mean, seriously, what's there to improve on? 
The transaction code is all normally totally pointless, and I merged the 
patch that avoids it when not necessary. 

It might be different if more people used "data=journal", but I don't 
doubt that is very common. For data=writeback and data=ordered, I bet 
generic_writepages() is as good as anything ext3-specific could be.

			Linus