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Commit d3bc1fef authored by Wu Fengguang's avatar Wu Fengguang
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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: default avatarJan Kara <jack@suse.cz>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
parent 54848d73

mm/page-writeback.c

+5 −8
Original line number Diff line number Diff line
@@ -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
@@ -1270,13 +1268,10 @@ 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)) {

	else if (unlikely(*p >= ratelimit_pages)) {

		*p = 0;

		ratelimit = 0;

	}

	}

	/*

	 * Pick up the dirtied pages by the exited tasks. This avoids lots of

	 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
@@ -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);