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    Subject[PATCH -V2 0/2] fix oom happening when changing cpuset'mems(was: [regression] cpuset,mm: update tasks' mems_allowed in time (58568d2))
    Nick Piggin reported that the allocator may see an empty nodemask when changing
    cpuset's mems[1]. It happens only on the kernel that do not do atomic nodemask_t

    But I found that there is also a problem on the kernel that can do atomic
    nodemask_t stores. The problem is that the allocator can't find a node to
    alloc page when changing cpuset's mems though there is a lot of free memory.
    The reason is like this:
    (mpol: mempolicy)
    task1 task1's mpol task2
    alloc page 1
    alloc on node0? NO 1
    1 change mems from 1 to 0
    1 rebind task1's mpol
    0-1 set new bits
    0 clear disallowed bits
    alloc on node1? NO 0
    can't alloc page
    goto oom

    I can use the attached program reproduce it by the following step:
    # mkdir /dev/cpuset
    # mount -t cpuset cpuset /dev/cpuset
    # mkdir /dev/cpuset/1
    # echo `cat /dev/cpuset/cpus` > /dev/cpuset/1/cpus
    # echo `cat /dev/cpuset/mems` > /dev/cpuset/1/mems
    # echo $$ > /dev/cpuset/1/tasks
    # numactl --membind=`cat /dev/cpuset/mems` ./cpuset_mem_hog <nr_tasks> &
    <nr_tasks> = max(nr_cpus - 1, 1)
    # killall -s SIGUSR1 cpuset_mem_hog
    # ./

    several hours later, oom will happen though there is a lot of free memory.

    This patchset fixes this problem by expanding the nodes range first(set newly
    allowed bits) and shrink it lazily(clear newly disallowed bits). So we use a
    variable to tell the write-side task that read-side task is reading nodemask,
    and the write-side task clears newly disallowed nodes after read-side task ends
    the current memory allocation.

    Changelog since V1:
    - restructure the mempolicy's rebind functions, and split the rebind work to
    two steps because the rebind functions may breaks the first step - expanding
    the nodes range.



    [PATCH 1/2] mempolicy: restructure rebinding-mempolicy functions
    [PATCH 2/2] cpuset,mm: fix no node to alloc memory when changing cpuset's mems
    [unhandled content-type:application/gzip]
     \ /
      Last update: 2010-05-04 12:55    [W:2.220 / U:0.004 seconds]
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