linux-ext4 - Re: [RFC][PATCH] set_page_buffer_dirty should skip unmapped buffers

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Date:	Fri, 8 Sep 2006 10:25:32 +0200
From:	Jan Kara <jack@...e.cz>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>,
	Anton Altaparmakov <aia21@....ac.uk>, sct@...hat.com,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC][PATCH] set_page_buffer_dirty should skip unmapped buffers

  Hi,

> Jan Kara wrote:
> >  I've been looking more at the code and I have revived my patch fixing
> >this part of the code. I've mildly tested the patch. Could you also give
> >it a try? Thanks.
> >
> >								Honza
> >  
> >------------------------------------------------------------------------
> >
> >Original commit code assumes, that when a buffer on BJ_SyncData list is 
> >locked,
> >it is being written to disk. But this is not true and hence it can lead to 
> >a
> >potential data loss on crash. Also the code didn't count with the fact that
> >journal_dirty_data() can steal buffers from committing transaction and 
> >hence
> >could write buffers that no longer belong to the committing transaction.
> >Finally it could possibly happen that we tried writing out one buffer 
> >several
> >times.
> >
> >The patch below tries to solve these problems by a complete rewrite of the 
> >data
> >commit code. We go through buffers on t_sync_datalist, lock buffers needing
> >write out and store them in an array. Buffers are also immediately refiled 
> >to
> >BJ_Locked list or unfiled (if the write out is completed). When the array 
> >is
> >full or we have to block on buffer lock, we submit all accumulated buffers 
> >for
> >IO.
> >
> >Signed-off-by: Jan Kara <jack@...e.cz>
> >
> >  
> I have been running 4+ hours with this patch and seems to work fine. I 
> haven't hit any
> assert yet :)
> 
> I will let it run till tomorrow. I will let you know, how it goes.
  Great, thanks. BTW: Do you have any performance tests handy? The
changes are big enough to cause some unexpected performance regressions,
livelocks... If you don't have anything ready, I can setup and run
something myself.  Just that I don't like this testing too much ;).

								Honza

-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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