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    Subject[patch 40/46] mm: write_cache_pages terminate quickly
    2.6.28-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Nick Piggin <npiggin@suse.de>

    commit d5482cdf8a0aacb1e6468a97d5544f5829c8d8c4 upstream.

    Terminate the write_cache_pages loop upon encountering the first page past
    end, without locking the page. Pages cannot have their index change when
    we have a reference on them (truncate, eg truncate_inode_pages_range
    performs the same check without the page lock).

    Signed-off-by: Nick Piggin <npiggin@suse.de>
    Cc: Chris Mason <chris.mason@oracle.com>
    Cc: Dave Chinner <david@fromorbit.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    mm/page-writeback.c | 32 ++++++++++++++++----------------
    1 file changed, 16 insertions(+), 16 deletions(-)

    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -911,15 +911,24 @@ retry:
    for (i = 0; i < nr_pages; i++) {
    struct page *page = pvec.pages[i];

    - done_index = page->index + 1;
    -
    /*
    - * At this point we hold neither mapping->tree_lock nor
    - * lock on the page itself: the page may be truncated or
    - * invalidated (changing page->mapping to NULL), or even
    - * swizzled back from swapper_space to tmpfs file
    - * mapping
    + * At this point, the page may be truncated or
    + * invalidated (changing page->mapping to NULL), or
    + * even swizzled back from swapper_space to tmpfs file
    + * mapping. However, page->index will not change
    + * because we have a reference on the page.
    */
    + if (page->index > end) {
    + /*
    + * can't be range_cyclic (1st pass) because
    + * end == -1 in that case.
    + */
    + done = 1;
    + break;
    + }
    +
    + done_index = page->index + 1;
    +
    lock_page(page);

    /*
    @@ -936,15 +945,6 @@ continue_unlock:
    continue;
    }

    - if (page->index > end) {
    - /*
    - * can't be range_cyclic (1st pass) because
    - * end == -1 in that case.
    - */
    - done = 1;
    - goto continue_unlock;
    - }
    -
    if (!PageDirty(page)) {
    /* someone wrote it for us */
    goto continue_unlock;


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