Commit a1c3bfb2 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

mm/page-writeback.c: do not count anon pages as dirtyable memory 



The VM is currently heavily tuned to avoid swapping.  Whether that is
good or bad is a separate discussion, but as long as the VM won't swap
to make room for dirty cache, we can not consider anonymous pages when
calculating the amount of dirtyable memory, the baseline to which
dirty_background_ratio and dirty_ratio are applied.

A simple workload that occupies a significant size (40+%, depending on
memory layout, storage speeds etc.) of memory with anon/tmpfs pages and
uses the remainder for a streaming writer demonstrates this problem.  In
that case, the actual cache pages are a small fraction of what is
considered dirtyable overall, which results in an relatively large
portion of the cache pages to be dirtied.  As kswapd starts rotating
these, random tasks enter direct reclaim and stall on IO.

Only consider free pages and file pages dirtyable.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reported-by: default avatarTejun Heo <tj@kernel.org>
Tested-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a804552b

include/linux/vmstat.h

+0 −2
Original line number Diff line number Diff line
@@ -142,8 +142,6 @@ static inline unsigned long zone_page_state_snapshot(struct zone *zone, 
	return x;

}



extern unsigned long global_reclaimable_pages(void);



#ifdef CONFIG_NUMA

/*

 * Determine the per node value of a stat item. This function

mm/internal.h

+0 −1
Original line number Diff line number Diff line
@@ -83,7 +83,6 @@ extern unsigned long highest_memmap_pfn; 
 */

extern int isolate_lru_page(struct page *page);

extern void putback_lru_page(struct page *page);

extern unsigned long zone_reclaimable_pages(struct zone *zone);

extern bool zone_reclaimable(struct zone *zone);



/*

mm/page-writeback.c

+4 −2
Original line number Diff line number Diff line
@@ -205,7 +205,8 @@ static unsigned long zone_dirtyable_memory(struct zone *zone) 
	nr_pages = zone_page_state(zone, NR_FREE_PAGES);

	nr_pages -= min(nr_pages, zone->dirty_balance_reserve);



	nr_pages += zone_reclaimable_pages(zone);

	nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);

	nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);



	return nr_pages;

}
@@ -258,7 +259,8 @@ static unsigned long global_dirtyable_memory(void) 
	x = global_page_state(NR_FREE_PAGES);

	x -= min(x, dirty_balance_reserve);



	x += global_reclaimable_pages();

	x += global_page_state(NR_INACTIVE_FILE);

	x += global_page_state(NR_ACTIVE_FILE);



	if (!vm_highmem_is_dirtyable)

		x -= highmem_dirtyable_memory(x);

mm/vmscan.c

+1 −22
Original line number Diff line number Diff line
@@ -147,7 +147,7 @@ static bool global_reclaim(struct scan_control *sc) 
}

#endif



unsigned long zone_reclaimable_pages(struct zone *zone)

static unsigned long zone_reclaimable_pages(struct zone *zone)

{

	int nr;
@@ -3315,27 +3315,6 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 
	wake_up_interruptible(&pgdat->kswapd_wait);

}



/*

 * The reclaimable count would be mostly accurate.

 * The less reclaimable pages may be

 * - mlocked pages, which will be moved to unevictable list when encountered

 * - mapped pages, which may require several travels to be reclaimed

 * - dirty pages, which is not "instantly" reclaimable

 */

unsigned long global_reclaimable_pages(void)

{

	int nr;



	nr = global_page_state(NR_ACTIVE_FILE) +

	     global_page_state(NR_INACTIVE_FILE);



	if (get_nr_swap_pages() > 0)

		nr += global_page_state(NR_ACTIVE_ANON) +

		      global_page_state(NR_INACTIVE_ANON);



	return nr;

}



#ifdef CONFIG_HIBERNATION

/*

 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of

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