linux-ext4 - Re: [PATCH 1/2] HACK: ext3: mount fast even when recovering

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Date:	Wed, 15 Jul 2009 18:35:38 +0300
From:	Adrian Hunter <adrian.hunter@...ia.com>
To:	Theodore Tso <tytso@....edu>
CC:	Eric Sandeen <sandeen@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"sct@...hat.com" <sct@...hat.com>,
	"adilger@....com" <adilger@....com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Bityutskiy Artem (Nokia-D/Helsinki)" <Artem.Bityutskiy@...ia.com>
Subject: Re: [PATCH 1/2] HACK: ext3: mount fast even when recovering

Theodore Tso wrote:
> On Tue, Jul 14, 2009 at 04:46:37PM -0500, Eric Sandeen wrote:
>> (whoa, can barriers make something faster?  who woulda thunk it)
> 
> I sent this reply in response to the first Adrian's first e-mail, that
> had bogus e-mail addresses for akpm and sct, so resending it here:

Sorry about that.

> Have you actually benchmarked these patches, ideally with a fixed
> filesystem image so the two runs are done requiring exactly the same
> number of blocks to recover?  We implement ordered I/O in terms of
> doing a flush, so it would be surprising to see that a significant
> difference in times.  Also, it would be useful to do a blktrace before
> and after your patches, again with a fixed filesystem image so the
> experiment can be carefully controlled.

Yes the I/O is no faster.

The hacks just make the file system available for reading while recovery I/O
is ongoing.

Attempts to write are likely to block (even buffered I/O must wait for
locked buffers).

I will send some examples.
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