On Fri, 2009-06-05 at 10:30 -0400, Dan Magenheimer wrote:
> Suggestion: Perhaps the balloon_timer interval should
> be configurable via sysfs?
Perhaps. It'd be preferable to have a default which Just Works though.
I'd be inclined to wait until someone has a concrete problem with the
interval and then decide whether the default simply needs adjusting or a
tuning nob is required.
I also thought about making it back-off on each successive failure but
decided that was getting ahead of myself too.
Ian.
>
> > -----Original Message-----
> > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxxxxx]
> > Sent: Friday, June 05, 2009 4:57 AM
> > To: xen-devel
> > Cc: Keir Fraser
> > Subject: [Xen-devel] linux: 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.
> >
> > This patch is for the 2.6.18-xen tree.
> >
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >
> > diff -r fd9c565657b8 drivers/xen/balloon/balloon.c
> > --- a/drivers/xen/balloon/balloon.c Thu Jun 04 16:26:49 2009 +0100
> > +++ b/drivers/xen/balloon/balloon.c Fri Jun 05 11:56:22 2009 +0100
> > @@ -188,7 +188,7 @@
> >
> > 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 @@
> > }
> >
> > 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;
> > + reservation.nr_extents = nr_pages;
> > + rc = HYPERVISOR_memory_op(XENMEM_populate_physmap,
> > &reservation);
> > + if (rc < 0)
> > + goto out;
> >
> > - /* 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);
> > - 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 @@
> > 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 @@
> > 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 @@
> > "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 @@
> > 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 -r fd9c565657b8 drivers/xen/balloon/common.h
> > --- a/drivers/xen/balloon/common.h Thu Jun 04 16:26:49 2009 +0100
> > +++ b/drivers/xen/balloon/common.h Fri Jun 05 11:56:22 2009 +0100
> > @@ -35,8 +35,6 @@
> > /* 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 -r fd9c565657b8 drivers/xen/balloon/sysfs.c
> > --- a/drivers/xen/balloon/sysfs.c Thu Jun 04 16:26:49 2009 +0100
> > +++ b/drivers/xen/balloon/sysfs.c Fri Jun 05 11:56:22 2009 +0100
> > @@ -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 @@
> > &attr_current_kb.attr,
> > &attr_low_kb.attr,
> > &attr_high_kb.attr,
> > - &attr_hard_limit_kb.attr,
> > &attr_driver_kb.attr,
> > NULL
> > };
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
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