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    SubjectRe: [PATCH 3/5] writeback: fix dirtied pages accounting on sub-page writes
    On Mon 21-11-11 21:03:45, Wu Fengguang wrote:
    > 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.
    Well, but after this change, the interface balance_dirty_ratelimited_nr()
    is strange because the argument is only used for per-CPU ratelimiting and
    not for per-task ratelimiting... So if you do this switch then I'd also
    switch bdp_ratelimits to get consistent results and a clean interface and
    completely kill balance_dirty_pages_ratelimited_nr().

    Honza

    >
    > 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);
    >
    >
    --
    Jan Kara <jack@suse.cz>
    SUSE Labs, CR


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