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    Subject[PATCH 3/5] writeback: fix dirtied pages accounting on sub-page writes
    When dd in 512bytes, generic_perform_write() calls
    balance_dirty_pages_ratelimited() 8 times for the same page, but
    obviously the page is only dirtied once.

    Fix it by accounting nr_dirtied at page dirty time.

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    mm/page-writeback.c | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    --- linux-next.orig/mm/page-writeback.c 2011-11-17 20:57:13.000000000 +0800
    +++ linux-next/mm/page-writeback.c 2011-11-17 20:57:15.000000000 +0800
    @@ -1224,8 +1224,6 @@ void balance_dirty_pages_ratelimited_nr(
    if (bdi->dirty_exceeded)
    ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));

    - current->nr_dirtied += nr_pages_dirtied;
    -
    preempt_disable();
    /*
    * This prevents one CPU to accumulate too many dirtied pages without
    @@ -1734,6 +1732,7 @@ void account_page_dirtied(struct page *p
    __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
    __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
    task_io_account_write(PAGE_CACHE_SIZE);
    + current->nr_dirtied++;
    }
    }
    EXPORT_SYMBOL(account_page_dirtied);



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