Re: Bug with "fix partial page writes" [3.2-rc regression]

[Allison Henderson]

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@xxxxxxxxxxxxxxxxxx> 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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