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

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Date:	Fri, 08 Sep 2006 07:35:22 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Jan Kara <jack@...e.cz>
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

Jan Kara wrote:
>   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 ;).
>   
Tests are still running fine.

I don't have any performance tests handy. We have some automated tests I 
can schedule
to run to verify the stability aspects.

Thanks,
Badari

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