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 tsk->nr_dirtied and bdp_ratelimits at page dirty time.

Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 619c445..5d1ef5d 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1258,8 +1258,6 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
        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
@@ -1270,12 +1268,9 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
        p =  &__get_cpu_var(bdp_ratelimits);
        if (unlikely(current->nr_dirtied >= ratelimit))
                *p = 0;
-       else {
-               *p += nr_pages_dirtied;
-               if (unlikely(*p >= ratelimit_pages)) {
-                       *p = 0;
-                       ratelimit = 0;
-               }
+       else if (unlikely(*p >= ratelimit_pages)) {
+               *p = 0;
+               ratelimit = 0;
        }
        /*
         * Pick up the dirtied pages by the exited tasks. This avoids lots of
@@ -1768,6 +1763,8 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
                __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++;
+               this_cpu_inc(bdp_ratelimits);
        }
 }
 EXPORT_SYMBOL(account_page_dirtied);