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Subject[PATCH] xen: Fix selfballooning and ensure it doesn't go too far
[PATCH] xen: Fix selfballooning and ensure it doesn't go too far

The balloon driver's "current_pages" is very different from
totalram_pages. Self-ballooning needs to be driven by
the latter. Also, Committed_AS doesn't account for pages
used by the kernel so enforce a floor for when there
are little or no user-space threads using memory.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>

diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
index 6ea852e..e3e48f1 100644
--- a/drivers/xen/xen-selfballoon.c
+++ b/drivers/xen/xen-selfballoon.c
@@ -195,14 +195,13 @@ __setup("selfballooning", xen_selfballooning_setup);
*/
static void selfballoon_process(struct work_struct *work)
{
- unsigned long cur_pages, goal_pages, tgt_pages;
+ unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
bool reset_timer = false;

if (xen_selfballooning_enabled) {
- cur_pages = balloon_stats.current_pages;
+ cur_pages = totalram_pages;
tgt_pages = cur_pages; /* default is no change */
- goal_pages = percpu_counter_read_positive(&vm_committed_as) +
- balloon_stats.current_pages - totalram_pages;
+ goal_pages = percpu_counter_read_positive(&vm_committed_as);
#ifdef CONFIG_FRONTSWAP
/* allow space for frontswap pages to be repatriated */
if (frontswap_selfshrinking && frontswap_enabled)
@@ -217,7 +216,13 @@ static void selfballoon_process(struct work_struct *work)
((goal_pages - cur_pages) /
selfballoon_uphysteresis);
/* else if cur_pages == goal_pages, no change */
- balloon_set_new_target(tgt_pages);
+ floor_pages = totalreserve_pages +
+ (roundup_pow_of_two(max_pfn) >> 5);
+ /* don't balloon too far, lest OOMs occur... */
+ if (tgt_pages < floor_pages)
+ tgt_pages = floor_pages;
+ balloon_set_new_target(tgt_pages +
+ balloon_stats.current_pages - totalram_pages);
reset_timer = true;
}
#ifdef CONFIG_FRONTSWAP

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