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    Subject[PATCH] unevictable mlocked pages: initialize mm member of munlock mm_walk structure
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    was: Re: [Bad page] trying to free locked page? (Re: [PATCH][RFC] fix
    kernel BUG at mm/migrate.c:719! in 2.6.26-rc5-mm3)

    On Tue, 2008-06-17 at 14:29 -0400, Lee Schermerhorn wrote:
    > On Tue, 2008-06-17 at 18:15 +0900, Daisuke Nishimura wrote:
    > > On Tue, 17 Jun 2008 18:03:14 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > > > On Tue, 17 Jun 2008 16:47:09 +0900
    > > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
    > > >
    > > > > On Tue, 17 Jun 2008 16:35:01 +0900, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
    > > > > > Hi.
    > > > > >
    > > > > > I got this bug while migrating pages only a few times
    > > > > > via memory_migrate of cpuset.
    > > > > >
    > > > > > Unfortunately, even if this patch is applied,
    > > > > > I got bad_page problem after hundreds times of page migration
    > > > > > (I'll report it in another mail).
    > > > > > But I believe something like this patch is needed anyway.
    > > > > >
    > > > >
    > > > > I got bad_page after hundreds times of page migration.
    > > > > It seems that a locked page is being freed.
    >
    > I'm seeing *mlocked* pages [PG_mlocked] being freed now with my stress
    > load, with just the "if(!page->mapping) { } clause removed, as proposed
    > in your rfc patch in previous mail. Need to investigate this...
    >
    <snip>

    This [freeing of mlocked pages] also occurs in unpatched 26-rc5-mm3.

    Fixed by the following:

    PATCH: fix munlock page table walk - now requires 'mm'

    Against 2.6.26-rc5-mm3.

    Incremental fix for: mlock-mlocked-pages-are-unevictable-fix.patch

    Initialize the 'mm' member of the mm_walk structure, else the
    page table walk doesn't occur, and mlocked pages will not be
    munlocked. This is visible in the vmstats:

    noreclaim_pgs_munlocked - should equal noreclaim_pgs_mlocked
    less (nr_mlock + noreclaim_pgs_cleared), but is always zero
    [munlock_vma_page() never called]

    noreclaim_pgs_mlockfreed - should be zero [for debug only],
    but == noreclaim_pgs_mlocked - (nr_mlock + noreclaim_pgs_cleared)


    Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

    mm/mlock.c | 2 ++
    1 file changed, 2 insertions(+)

    Index: linux-2.6.26-rc5-mm3/mm/mlock.c
    ===================================================================
    --- linux-2.6.26-rc5-mm3.orig/mm/mlock.c 2008-06-17 15:20:57.000000000 -0400
    +++ linux-2.6.26-rc5-mm3/mm/mlock.c 2008-06-17 15:23:17.000000000 -0400
    @@ -318,6 +318,8 @@ static void __munlock_vma_pages_range(st
    VM_BUG_ON(start < vma->vm_start);
    VM_BUG_ON(end > vma->vm_end);

    + munlock_page_walk.mm = mm;
    +
    lru_add_drain_all(); /* push cached pages to LRU */
    walk_page_range(start, end, &munlock_page_walk);
    lru_add_drain_all(); /* to update stats */




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