From ab13e13f19aaed7a5b6143b9c6e1d41e65a8f71e Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Fri, 5 Jun 2009 14:01:20 +0100 Subject: [PATCH] balloon: try harder to balloon up under memory pressure. Currently if the balloon driver is unable to increase the guest's reservation it assumes the failure was due to reaching its full allocation, gives up on the ballooning operation and records the limit it reached as the "hard limit". The driver will not try again until the target is set again (even to the same value). However it is possible that ballooning has in fact failed due to memory pressure in the host and therefore it is desirable to keep attempting to reach the target in case memory becomes available. The most likely scenario is that some guests are ballooning down while others are ballooning up and therefore there is temporary memory pressure while things stabilise. You would not expect a well behaved toolstack to ask a domain to balloon to more than its allocation nor would you expect it to deliberately over-commit memory by setting balloon targets which exceed the total host memory. This patch drops the concept of a hard limit and causes the balloon driver to retry increasing the reservation on a timer in the same manner as when decreasing the reservation. Also if we partially succeed in increasing the reservation (i.e. receive less pages than we asked for) then we may as well keep those pages rather than returning them to Xen. Signed-off-by: Ian Campbell --- drivers/xen/balloon/balloon.c | 38 ++++++++--------------------------- drivers/xen/balloon/common.h | 2 -- drivers/xen/balloon/sysfs.c | 4 ---- 3 files changed, 8 insertions(+), 36 deletions(-) diff --git a/drivers/xen/balloon/balloon.c b/drivers/xen/balloon/balloon.c index f2fbf318..0bb27345 100644 --- a/drivers/xen/balloon/balloon.c +++ b/drivers/xen/balloon/balloon.c @@ -188,7 +188,7 @@ static void balloon_alarm(unsigned long unused) static unsigned long current_target(void) { - unsigned long target = min(bs.target_pages, bs.hard_limit); + unsigned long target = bs.target_pages; if (target > (bs.current_pages + bs.balloon_low + bs.balloon_high)) target = bs.current_pages + bs.balloon_low + bs.balloon_high; return target; @@ -255,26 +255,12 @@ static int increase_reservation(unsigned long nr_pages) } set_xen_guest_handle(reservation.extent_start, frame_list); - reservation.nr_extents = nr_pages; - rc = HYPERVISOR_memory_op( - XENMEM_populate_physmap, &reservation); - if (rc < nr_pages) { - if (rc > 0) { - int ret; - - /* We hit the Xen hard limit: reprobe. */ - reservation.nr_extents = rc; - ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, - &reservation); - BUG_ON(ret != rc); - } - if (rc >= 0) - bs.hard_limit = (bs.current_pages + rc - - bs.driver_pages); + reservation.nr_extents = nr_pages; + rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation); + if (rc < 0) goto out; - } - for (i = 0; i < nr_pages; i++) { + for (i = 0; i < rc; i++) { page = balloon_retrieve(); BUG_ON(page == NULL); @@ -302,13 +288,13 @@ static int increase_reservation(unsigned long nr_pages) balloon_free_page(page); } - bs.current_pages += nr_pages; + bs.current_pages += rc; totalram_pages = bs.current_pages; out: balloon_unlock(flags); - return 0; + return rc < 0 ? rc : rc != nr_pages; } static int decrease_reservation(unsigned long nr_pages) @@ -420,7 +406,6 @@ static void balloon_process(void *unused) void balloon_set_new_target(unsigned long target) { /* No need for lock. Not read-modify-write updates. */ - bs.hard_limit = ~0UL; bs.target_pages = max(target, minimum_target()); schedule_work(&balloon_worker); } @@ -498,17 +483,11 @@ static int balloon_read(char *page, char **start, off_t off, "Requested target: %8lu kB\n" "Low-mem balloon: %8lu kB\n" "High-mem balloon: %8lu kB\n" - "Driver pages: %8lu kB\n" - "Xen hard limit: ", + "Driver pages: %8lu kB\n", PAGES2KB(bs.current_pages), PAGES2KB(bs.target_pages), PAGES2KB(bs.balloon_low), PAGES2KB(bs.balloon_high), PAGES2KB(bs.driver_pages)); - if (bs.hard_limit != ~0UL) - len += sprintf(page + len, "%8lu kB\n", - PAGES2KB(bs.hard_limit)); - else - len += sprintf(page + len, " ??? kB\n"); *eof = 1; return len; @@ -539,7 +518,6 @@ static int __init balloon_init(void) bs.balloon_low = 0; bs.balloon_high = 0; bs.driver_pages = 0UL; - bs.hard_limit = ~0UL; init_timer(&balloon_timer); balloon_timer.data = 0; diff --git a/drivers/xen/balloon/common.h b/drivers/xen/balloon/common.h index 4496d215..cf5d86f1 100644 --- a/drivers/xen/balloon/common.h +++ b/drivers/xen/balloon/common.h @@ -35,8 +35,6 @@ struct balloon_stats { /* We aim for 'current allocation' == 'target allocation'. */ unsigned long current_pages; unsigned long target_pages; - /* We may hit the hard limit in Xen. If we do then we remember it. */ - unsigned long hard_limit; /* * Drivers may alter the memory reservation independently, but they * must inform the balloon driver so we avoid hitting the hard limit. diff --git a/drivers/xen/balloon/sysfs.c b/drivers/xen/balloon/sysfs.c index 16411cbc..5aceedff 100644 --- a/drivers/xen/balloon/sysfs.c +++ b/drivers/xen/balloon/sysfs.c @@ -53,9 +53,6 @@ BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(bs.current_pages)); BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(bs.balloon_low)); BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(bs.balloon_high)); -BALLOON_SHOW(hard_limit_kb, - (bs.hard_limit!=~0UL) ? "%lu\n" : "???\n", - (bs.hard_limit!=~0UL) ? PAGES2KB(bs.hard_limit) : 0); BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(bs.driver_pages)); static ssize_t show_target_kb(struct sys_device *dev, char *buf) @@ -96,7 +93,6 @@ static struct attribute *balloon_info_attrs[] = { &attr_current_kb.attr, &attr_low_kb.attr, &attr_high_kb.attr, - &attr_hard_limit_kb.attr, &attr_driver_kb.attr, NULL }; -- 2.39.5