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    Subject[PATCH 1/9] ksm: fix mlockfreed to munlocked
    When KSM merges an mlocked page, it has been forgetting to munlock it:
    that's been left to free_page_mlock(), which reports it in /proc/vmstat
    as unevictable_pgs_mlockfreed instead of unevictable_pgs_munlocked (and
    whinges "Page flag mlocked set for process" in mmotm, whereas mainline
    is silently forgiving). Call munlock_vma_page() to fix that.

    Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    ---
    Is this a fix that I ought to backport to 2.6.32? It does rely on part of
    an earlier patch (moved unlock_page down), so does not apply cleanly as is.

    mm/internal.h | 3 ++-
    mm/ksm.c | 4 ++++
    mm/mlock.c | 4 ++--
    3 files changed, 8 insertions(+), 3 deletions(-)

    --- ksm0/mm/internal.h 2009-11-14 10:17:02.000000000 +0000
    +++ ksm1/mm/internal.h 2009-11-22 20:39:56.000000000 +0000
    @@ -105,9 +105,10 @@ static inline int is_mlocked_vma(struct
    }

    /*
    - * must be called with vma's mmap_sem held for read, and page locked.
    + * must be called with vma's mmap_sem held for read or write, and page locked.
    */
    extern void mlock_vma_page(struct page *page);
    +extern void munlock_vma_page(struct page *page);

    /*
    * Clear the page's PageMlocked(). This can be useful in a situation where
    --- ksm0/mm/ksm.c 2009-11-14 10:17:02.000000000 +0000
    +++ ksm1/mm/ksm.c 2009-11-22 20:39:56.000000000 +0000
    @@ -34,6 +34,7 @@
    #include <linux/ksm.h>

    #include <asm/tlbflush.h>
    +#include "internal.h"

    /*
    * A few notes about the KSM scanning process,
    @@ -762,6 +763,9 @@ static int try_to_merge_one_page(struct
    pages_identical(page, kpage))
    err = replace_page(vma, page, kpage, orig_pte);

    + if ((vma->vm_flags & VM_LOCKED) && !err)
    + munlock_vma_page(page);
    +
    unlock_page(page);
    out:
    return err;
    --- ksm0/mm/mlock.c 2009-11-14 10:17:02.000000000 +0000
    +++ ksm1/mm/mlock.c 2009-11-22 20:39:56.000000000 +0000
    @@ -99,14 +99,14 @@ void mlock_vma_page(struct page *page)
    * not get another chance to clear PageMlocked. If we successfully
    * isolate the page and try_to_munlock() detects other VM_LOCKED vmas
    * mapping the page, it will restore the PageMlocked state, unless the page
    - * is mapped in a non-linear vma. So, we go ahead and SetPageMlocked(),
    + * is mapped in a non-linear vma. So, we go ahead and ClearPageMlocked(),
    * perhaps redundantly.
    * If we lose the isolation race, and the page is mapped by other VM_LOCKED
    * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap()
    * either of which will restore the PageMlocked state by calling
    * mlock_vma_page() above, if it can grab the vma's mmap sem.
    */
    -static void munlock_vma_page(struct page *page)
    +void munlock_vma_page(struct page *page)
    {
    BUG_ON(!PageLocked(page));


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