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Date: Tue, 27 Sep 2011 16:57:44 +0100
From: David Vrabel <david.vrabel@...rix.com>
To: Dan Magenheimer <dan.magenheimer@...cle.com>
CC: Konrad Wilk <konrad.wilk@...cle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH v2] xen: Fix selfballooning and ensure it doesn't go too
far
On 27/09/11 16:03, Dan Magenheimer wrote:
> Note: This patch is also now in a git tree at:
>
> git://oss.oracle.com/git/djm/tmem.git#selfballoon-fix-v2
>
> The balloon driver's "current_pages" is very different from
> totalram_pages. Self-ballooning needs to be driven by
> the latter.
I don't think this part of the change makes any difference. It looks like it
rearranges the maths without changing the end result (other than
slightly increasing the rate of change).
I think this (partial, untested) patch is equivalent:
diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
index 1b4afd8..b207e89 100644
--- a/drivers/xen/xen-selfballoon.c
+++ b/drivers/xen/xen-selfballoon.c
@@ -194,14 +194,15 @@ __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, rsvd_pages, floor_pages;
bool reset_timer = false;
if (xen_selfballooning_enabled) {
cur_pages = balloon_stats.current_pages;
tgt_pages = cur_pages; /* default is no change */
- goal_pages = percpu_counter_read_positive(&vm_committed_as) +
- balloon_stats.current_pages - totalram_pages;
+ rsvd_pages = cur_pages - totalram_pages;
+ goal_pages = percpu_counter_read_positive(&vm_committed_as)
+ + rsvd_pages;
#ifdef CONFIG_FRONTSWAP
/* allow space for frontswap pages to be repatriated */
if (frontswap_selfshrinking && frontswap_enabled)
@@ -216,6 +217,11 @@ static void selfballoon_process(struct work_struct *work)
((goal_pages - cur_pages) /
selfballoon_uphysteresis);
/* else if cur_pages == goal_pages, no change */
+ floor_pages = rsvd_pages + totalreserve_pages +
+ ((roundup_pow_of_two(max_pfn) / 128) *
+ selfballoon_safety_margin);
+ if (tgt_pages < floor_pages)
+ tgt_pages = floor_pages;
balloon_set_new_target(tgt_pages);
reset_timer = true;
}
> 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. The floor function
> includes a "safety margin" tuneable in case we discover later
> that the floor function is still too aggressive in some workloads,
> though likely it will not be needed.
The sysfs file isn't documented (but then neither are any of the other
(self-)balloon driver sysfs files).
I don't think "safety_margin" is the right name. Perhaps,
"min_reservation_ratio" or something like that?
David
> Changes since version 1:
> - tuneable safety margin added
>
> [v2: konrad.wilk@...cle.com: make safety margin tuneable]
>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
>
> diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
> index 6ea852e..ceaada6 100644
> --- a/drivers/xen/xen-selfballoon.c
> +++ b/drivers/xen/xen-selfballoon.c
> @@ -93,6 +93,12 @@ static unsigned int selfballoon_uphysteresis __read_mostly = 1;
> /* In HZ, controls frequency of worker invocation. */
> static unsigned int selfballoon_interval __read_mostly = 5;
>
> +/*
> + * Scale factor for safety margin for minimum selfballooning target for balloon.
> + * Default adds about 3% (4/128) of max_pfn.
> + */
> +static unsigned int selfballoon_safety_margin = 4;
> +
> static void selfballoon_process(struct work_struct *work);
> static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
>
> @@ -195,14 +201,13 @@ __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 +222,13 @@ 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) / 128) *
> + selfballoon_safety_margin);
> + 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
> @@ -340,6 +351,30 @@ static ssize_t store_selfballoon_uphys(struct sys_device *dev,
> static SYSDEV_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
> show_selfballoon_uphys, store_selfballoon_uphys);
>
> +SELFBALLOON_SHOW(selfballoon_safety_margin, "%d\n", selfballoon_safety_margin);
> +
> +static ssize_t store_selfballoon_safety_margin(struct sys_device *dev,
> + struct sysdev_attribute *attr,
> + const char *buf,
> + size_t count)
> +{
> + unsigned long val;
> + int err;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> + err = strict_strtoul(buf, 10, &val);
> + if (err || val == 0 || val > 128)
> + return -EINVAL;
> + selfballoon_safety_margin = val;
> + return count;
> +}
> +
> +static SYSDEV_ATTR(selfballoon_safety_margin, S_IRUGO | S_IWUSR,
> + show_selfballoon_safety_margin,
> + store_selfballoon_safety_margin);
> +
> +
> #ifdef CONFIG_FRONTSWAP
> SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
>
> @@ -421,6 +456,7 @@ static struct attribute *selfballoon_attrs[] = {
> &attr_selfballoon_interval.attr,
> &attr_selfballoon_downhysteresis.attr,
> &attr_selfballoon_uphysteresis.attr,
> + &attr_selfballoon_safety_margin.attr,
> #ifdef CONFIG_FRONTSWAP
> &attr_frontswap_selfshrinking.attr,
> &attr_frontswap_hysteresis.attr,
--
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