Message-ID: <4EE046C7.9030902@linux.vnet.ibm.com>
Date:	Wed, 07 Dec 2011 22:10:31 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
CC:	Hugh Dickins <hughd@...gle.com>, "Ted Ts'o" <tytso@....edu>,
	Curt Wohlgemuth <curtw@...gle.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Rafael Wysocki <rjw@...k.pl>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andy Whitcroft <apw@...onical.com>
Subject: Re: Bug with "fix partial page writes" [3.2-rc regression]

On 12/07/2011 10:04 AM, Allison Henderson wrote:
> On 12/07/2011 01:28 AM, Yongqiang Yang wrote:
>> Hi Allison and Hugh,
>>
>> I think I found the problem and it has nothing to do with punching
>> hole. The patch [ext4: let ext4_bio_write_page handle EOF correctly]
>> would fix up the problem.
>>
>> I post the patch so that it can be tested as early as possible. The
>> problem has not appeared on my machine since the patch is applied.
>>
>> Yongqiang.
>
> Great! I will try it out with your other set in my sandbox and let you
> know what happens. Thx!
>
> Allison Henderson

Well, it's been running several hours now with out problems, so I think 
it will be ok, but I will let it run the full day.

Andy, I know you were also seeing issues in this area.  Could you try 
Yongqiang patches?  The code you were modifying needed to be removed, so 
I think they will resolve the issues you were seeing too.  Please try 
the following patch sets:

[PATCH 1/2] ext4: let mpage_submit_io works well when blocksize < pagesize
[PATCH 2/2] ext4: let ext4_discard_partial_buffers handle pages without 
buffers correctly

and

[PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized
[PATCH 2/2] ext4: let ext4_bio_write_page handle EOF correctly

Thx!

Allison Henderson

>
>> On Wed, Dec 7, 2011 at 5:15 AM, Allison Henderson
>> <achender@...ux.vnet.ibm.com> wrote:
>>> On 12/06/2011 01:55 AM, Hugh Dickins wrote:
>>>>
>>>> On Mon, 5 Dec 2011, Allison Henderson wrote:
>>>>>
>>>>> On 12/05/2011 04:38 PM, Hugh Dickins wrote:
>>>>>>
>>>>>>
>>>>>> This has been outstanding for a month now, and we've heard no
>>>>>> progress:
>>>>>> please revert commit 02fac1297eb3 "ext4: fix partial page writes" for
>>>>>> rc5.
>>>>>>
>>>>>> The problems appear on a 1k-blocksize filesystem under memory
>>>>>> pressure:
>>>>>> the hunk in ext4_da_write_end() causes oops, because it's playing
>>>>>> with
>>>>>> a page after generic_write_end() dropped our last reference to it;
>>>>>> and
>>>>>> backing out the hunk in ext4_da_write_begin() is then found to stop
>>>>>> rare data corruption seen when kbuilding.
>>>>>>
>>>>>> Although I earlier reported that backing out the patch caused an fsx
>>>>>> test to fail earlier, I've since found great variation in how soon it
>>>>>> fails, and seen it fail just as quickly with 02fac1297eb3 still in.
>>>>>> I also reported that I had to go back to 2.6.38 for fsx not to fail
>>>>>> under memory pressure: you won't be surprised that that turned out to
>>>>>> be because 2.6.38 defaults nomblk_io_submit but 2.6.39
>>>>>> mblk_io_submit.
>>>>>
>>>>>
>>>>> Have you tried Yongqiang's patch "[PATCH 1/2] ext4: let
>>>>> mpage_submit_io
>>>>> works well when blocksize< pagesize" ? I have tried it and it does
>>>>> seem
>>>>> to
>>>>> help, but I am still running into some failures that I am trying to
>>>>> debug,
>>>>> but let please let us know if it helps the issues that you are seeing.
>>>>> Thx!
>>>>
>>>>
>>>> That 1/2, or the 2/2 "ext4: let ext4_discard_partial_buffers handle
>>>> pages without buffers correctly"? The latter is mostly a reversion
>>>> of your 02fac1297eb3, so that's the one I need to fix the oops and
>>>> rare data corruption. Perhaps you're suggesting 1/2 for fsx failures
>>>> under memory pressure?
>>>>
>>>> I've now tried the fsx test on three machines, with both 1/2 and 2/2
>>>> applied to 3.2-rc4. On one machine, with ext2 on loop on tmpfs, the
>>>> fsx test failed in a couple of minutes with those patches; on another
>>>> machine, with ext2 on loop on tmpfs, it failed after about 40 minutes
>>>> with the patches; on this laptop, with ext2 on SSD, it's just now
>>>> failed after 35 minutes with the patches.
>>>>
>>>> That's not to say that Yongqiang's patches aren't good; but I cannot
>>>> detect whether they make any improvement or not, since lasting for 2 or
>>>> 40 minutes is typical for fsx under memory pressure with recent
>>>> kernels.
>>>
>>>
>>>
>>> Well, initially I meant to just try the whole set, but now that I try
>>> just
>>> one of them, I find that I get further with only the first one. I think
>>> Yongqiang and I have a similar set up because I get the hang if I
>>> dont have
>>> the first patch, and I get the fsx write failure (in about 20 or so
>>> minutes)
>>> if I have the second one. But I think Yongqiang's right, we need to
>>> figure
>>> out why the page is uptodate when it shouldn't be.
>>>
>>>
>>>>
>>>> Hugh
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>>>
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>>
>>
>>
>
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