The access ratio based scan rate determination in get_scan_ratio

works ok in most situations, but needs to be corrected in some

corner cases:

- if we run out of swap space, do not bother scanning the anon LRUs

- if we have already freed all of the page cache, we need to scan

  the anon LRUs
Signed-off-by: Rik van Riel <riel@redhat.com>
Index: linux-2.6.24-rc6-mm1/mm/vmscan.c

===================================================================

--- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c	2008-01-07 17:33:50.000000000 -0500

+++ linux-2.6.24-rc6-mm1/mm/vmscan.c	2008-01-07 17:57:49.000000000 -0500

@@ -1182,7 +1182,7 @@ static unsigned long shrink_list(enum lr

 static void get_scan_ratio(struct zone *zone, struct scan_control * sc,

 					unsigned long *percent)

 {

-	unsigned long anon, file;

+	unsigned long anon, file, free;

 	unsigned long anon_prio, file_prio;

 	unsigned long rotate_sum;

 	unsigned long ap, fp;

@@ -1230,6 +1230,20 @@ static void get_scan_ratio(struct zone *

 	else if (fp > 100)

 		fp = 100;

 	percent[1] = fp;

+

+	free = zone_page_state(zone, NR_FREE_PAGES);

+

+	/*

+	 * If we have no swap space, do not bother scanning anon pages

+	 */

+	if (nr_swap_pages <= 0)

+		percent[0] = 0;

+	/*

+	 * If we already freed most file pages, scan the anon pages

+	 * regardless of the page access ratios or swappiness setting.

+	 */

+	else if (file + free <= zone->pages_high)

+		percent[0] = 100;

 }
--

All Rights Reversed
--

On Tue, 08 Jan 2008 15:59:46 -0500

Doesn't this mean that swap-cache in ACTIVE_ANON_LIST is not scanned ?

Or swap-cache is in File-Cache list ?
Thanks,

-Kame
--

On Wed, 9 Jan 2008 13:16:42 +0900
You are right, the swap cache will not be scanned once we run

completely out of swap space.  To compensate for that, this

patch series has a patch that does scanning of swap cache and

freeing of swap space used by pages on the LRU list while there

is still space free.
Scanning all of the anon LRU lists could be a lot of work for

very little gain.  A typical large server will have 32GB or

more of RAM, but only the default 2GB of swap.
All we accomplish by scanning the anonymous memory on a system

like that (once swap is full) is eating up CPU time and causing

lock contention.
--

All rights reversed.

--