linux-ext4 - Re: DIO process stuck apparently due to dioread

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Message-ID: <4E4CB5F0.6000202@msgid.tls.msk.ru>
Date:	Thu, 18 Aug 2011 10:49:20 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Ted Ts'o <tytso@....edu>
CC:	Jiaying Zhang <jiayingz@...gle.com>, Tao Ma <tm@....ma>,
	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	sandeen@...hat.com
Subject: Re: DIO process stuck apparently due to dioread_nolock (3.0)

17.08.2011 21:02, Ted Ts'o wrote:
[]
> What I'd like to do long-term here is to change things so that (a)
> instead of instantiating the extent as uninitialized, writing the
> data, and then doing the uninit->init conversion to writing the data
> and then instantiated the extent as initialzied.  This would also
> allow us to get rid of data=ordered mode.  And we should make it work
> for fs block size != page size.
> 
> It means that we need a way of adding this sort of information into an
> in-memory extent cache but which isn't saved to disk until the data is
> written.  We've also talked about adding the information about whether
> an extent is subject to delalloc as well, so we don't have to grovel
> through the page cache and look at individual buffers attached to the
> pages.  And there are folks who have been experimenting with an
> in-memory extent tree cache to speed access to fast PCIe-attached
> flash.
> 
> It seems to me that if we're careful a single solution should be able
> to solve all of these problems...

What about current situation, how do you think - should it be ignored
for now, having in mind that dioread_nolock isn't used often (but it
gives _serious_ difference in read speed), or, short term, fix this
very case which have real-life impact already, while implementing a
long-term solution?

Thank you!

/mjt
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