From d4c7abdff73090a98e64d11dada4911ec29bcaea Mon Sep 17 00:00:00 2001 From: Bob Liu Date: Mon, 17 Feb 2014 19:11:39 +0800 Subject: [PATCH] drivers:xen-selfballoon:reset 'frontswap_inertia_counter' after frontswap_shrink When I looked at this issue https://lkml.org/lkml/2013/11/21/158, I found that frontswap_selfshrink() doesn't work as expected sometimes. Pages are continuously added to frontswap and gotten back soon. It's a waste of cpu time and increases the memory pressue of Guest OS. Take an example. First time in frontswap_selfshrink(): 1. last_frontswap_pages = cur_frontswap_pages = 0 2. cur_frontswap_pages = frontswap_curr_pages() = 100 When 'frontswap_inertia_counter' decreased to 0: 1. last_frontswap_pages = cur_frontswap_pages = 100 2. cur_frontswap_pages = frontswap_curr_pages() = 100 3. call frontswap_shrink() and let's assumption that 10 pages are gotten back from frontswap. 4. now frontswap_curr_pages() is 90. If then memory is not enough in Guest OS and 9 more pages(smaller than gotten back) added to frontswap. Now frontswap_curr_pages() is 99 and we don't expect to get back more pages from frontswap because geust os is under memory pressure. But next time in frontswap_selfshrink(): 1. last_frontswap_pages is set to the old value of cur_frontswap_pages(still 100) 2. cur_frontswap_pages(99) is still smaller than last_frontswap_pages. 3. call frontswap_shrink() and continue to get back pages from frontswap!! Signed-off-by: Bob Liu Signed-off-by: Konrad Rzeszutek Wilk --- drivers/xen/xen-selfballoon.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c index 745ad79c1d8e..3b2bffde534f 100644 --- a/drivers/xen/xen-selfballoon.c +++ b/drivers/xen/xen-selfballoon.c @@ -170,6 +170,7 @@ static void frontswap_selfshrink(void) tgt_frontswap_pages = cur_frontswap_pages - (cur_frontswap_pages / frontswap_hysteresis); frontswap_shrink(tgt_frontswap_pages); + frontswap_inertia_counter = frontswap_inertia; } #endif /* CONFIG_FRONTSWAP */ -- 2.20.1