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    SubjectRe: Bug with "fix partial page writes" [3.2-rc regression]
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    On Tue, Dec 6, 2011 at 11:33 AM, Tao Ma <tm@tao.ma> wrote:
    > On 12/06/2011 11:08 AM, Yongqiang Yang wrote:
    >> Hi Allison,
    >>
    >> I noticed another problem which has nothing to do with punching hole.
    >>  __block_write_begin does not zero buffers beyond EOF.(I guess you
    > yes, that is expected.
    >> tried to zero them in your code, am I right? )  When users mapread
    >> beyond EOF,  users get non-zero data.  I am not sure zero or non-zero
    >> data should be, but fsx thinks they should be zero data and reports an
    >> error.
    > why users can read the data passing EOF? I am also puzzled. Punching
    > hole will do this? I don't think it's right.
    According to code, fiemap_fault handles the case right. But I met
    the error - 'non-zero data beyond EOF' reported by fsx. It is
    strange. It seems that uptodate status is set wrong. Just a guess:-)

    I am guessing Allison met the problem before and tried to fix it in
    write path by zeroing buffers beyond EOF.

    Yongqiang.
    >
    > Thanks
    > Tao
    >>
    >> It I understand the problem right, it happens more often with punch hole.
    >>
    >> Yongqiang.
    >> On Tue, Dec 6, 2011 at 9:40 AM, Allison Henderson
    >> <achender@linux.vnet.ibm.com> wrote:
    >>> On 12/05/2011 04:38 PM, Hugh Dickins wrote:
    >>>>
    >>>> On Mon, 21 Nov 2011, Hugh Dickins wrote:
    >>>>>
    >>>>> On Mon, 21 Nov 2011, Ted Ts'o wrote:
    >>>>>>
    >>>>>> On Sun, Nov 20, 2011 at 12:59:10PM -0800, Hugh Dickins wrote:
    >>>>>>>
    >>>>>>> On Tue, 8 Nov 2011, Curt Wohlgemuth wrote:
    >>>>>>> It appears that there's a bug with this patch:
    >>>>
    >>>>
    >>>> 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.
    >>>>
    >>>> Thanks,
    >>>> Hugh
    >>>>
    >>>
    >>>
    >>> Hi there,
    >>>
    >>> 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!
    >>>
    >>> Allison Henderson
    >>>
    >>
    >>
    >>
    >



    --
    Best Wishes
    Yongqiang Yang
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