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

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

[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@xxxxxxxxxx>

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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