linux-kernel - Re: [PATCH] clear PageError bit in msync & fsync

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Message-ID: <20101109210715.GJ3099@thunk.org>
Date:	Tue, 9 Nov 2010 16:07:15 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Rik van Riel <riel@...hat.com>
Cc:	Jeff Layton <jlayton@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, esandeen@...hat.com, jmoyer@...hat.com,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] clear PageError bit in msync & fsync

On Tue, Nov 09, 2010 at 02:33:29PM -0500, Rik van Riel wrote:
> 
> There are essentially two possibilities:
> 1) the VM can potentially be filled up with uncleanable dirty pages, or
> 2) pages that hit an IO error are left in a clean state, so they can
>    be reclaimed under memory pressure
> 
> Alternative 1 could cause the entire system to deadlock, while
> option 2 puts the onus on userland apps to rewrite the data
> from a failed msync/fsync.
> 
> Currently the VM has behaviour #2 which is preserved with my
> patch.
> 
> The only difference with my patch is, we won't keep returning
> -EIO on subsequent, error free, msync or fsync calls to files
> that had an IO error at some previous point in the past.

Do we guarantee that the application will get EIO at least once?  I
thought there were issues where the error bit could get lost if the
page writeback was triggered by sync() run by a third-party
application.


     	       	   	     		- Ted
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