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    SubjectRe: ftruncate-mmap: pages are lost after writing to mmaped file.
    On Thu, Apr 2, 2009 at 8:51 AM, Nick Piggin <> wrote:
    > On Thursday 02 April 2009 22:34:01 Jan Kara wrote:
    >> On Thu 02-04-09 22:24:29, Nick Piggin wrote:
    >> > On Thursday 02 April 2009 09:36:13 Ying Han wrote:
    >> > > Hi Jan:
    >> > > I feel that the problem you saw is kind of differnt than mine. As
    >> > > you mentioned that you saw the PageError() message, which i don't see
    >> > > it on my system. I tried you patch(based on 2.6.21) on my system and
    >> > > it runs ok for 2 days, Still, since i don't see the same error message
    >> > > as you saw, i am not convineced this is the root cause at least for
    >> > > our problem. I am still looking into it.
    >> > > So, are you seeing the PageError() every time the problem happened?
    >> >
    >> > So I asked if you could test with my workaround of taking truncate_mutex
    >> > at the start of ext2_get_blocks, and report back. I never heard of any
    >> > response after that.
    >> >
    >> > To reiterate: I was able to reproduce a problem with ext2 (I was testing
    >> > on brd to get IO rates high enough to reproduce it quite frequently).
    >> > I think I narrowed the problem down to block allocation or inode block
    >> > tree corruption because I was unable to reproduce it with that hack in
    >> > place.
    >> Nick, what load did you use for reproduction? I'll try to reproduce it
    >> here so that I can debug ext2...
    > OK, I set up the filesystem like this:
    > modprobe rd rd_size=$[3*1024*1024] #almost fill memory so we reclaim buffers
    > dd if=/dev/zero of=/dev/ram0 bs=4k #prefill brd so we don't get alloc deadlock
    > mkfs.ext2 -b1024 /dev/ram0 #1K buffers
    > Test is basically unmodified except I use 64MB files, and start 8 of them
    > at once to (8 core system, so improve chances of hitting the bug). Although I
    > do see it with only 1 running it takes longer to trigger.
    > I also run a loop doing 'sync ; echo 3 > /proc/sys/vm/drop_caches' but I don't
    > know if that really helps speed up reproducing it. It is quite random to hit,
    > but I was able to hit it IIRC in under a minute with that setup.

    Here is how i reproduce it:
    Filesystem is ext2 with blocksize 4096
    Fill up the ram with 95% anon memory and mlockall ( put enough memory
    pressure which will trigger page reclaim and background writeout)
    Run one thread of the test program

    and i will see "bad pages" within few minutes.


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      Last update: 2009-04-02 19:47    [W:0.026 / U:5.464 seconds]
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