* [PATCH] mm/damon/core: Avoid fake load reports due to uninterruptible sleeps
@ 2021-11-24 14:52 SeongJae Park
2021-11-24 21:42 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: SeongJae Park @ 2021-11-24 14:52 UTC (permalink / raw)
To: akpm; +Cc: shakeelb, linux-mm, linux-kernel, SeongJae Park, stable
Because DAMON sleeps in uninterruptible mode, /proc/loadavg reports fake
load while DAMON is turned on, though it is doing nothing. This can
confuse users[1]. To avoid the case, this commit makes DAMON sleeps in
idle mode.
[1] https://lore.kernel.org/all/11868371.O9o76ZdvQC@natalenko.name/
Fixes: 2224d8485492 ("mm: introduce Data Access MONitor (DAMON)")
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.15.x
---
I think this needs to be applied on v5.15.y, but this cannot cleanly
applied there as is. I will back-port this on v5.15.y and post later
once this is merged in the mainline.
mm/damon/core.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c
index daacd9536c7c..7813f47aadc9 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -12,6 +12,8 @@
#include <linux/kthread.h>
#include <linux/mm.h>
#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
#include <linux/slab.h>
#include <linux/string.h>
@@ -976,12 +978,25 @@ static unsigned long damos_wmark_wait_us(struct damos *scheme)
return 0;
}
+/* sleep for @usecs in idle mode */
+static void __sched damon_usleep_idle(unsigned long usecs)
+{
+ ktime_t exp = ktime_add_us(ktime_get(), usecs);
+ u64 delta = usecs * NSEC_PER_USEC / 100; /* allow 1% error */
+
+ for (;;) {
+ __set_current_state(TASK_IDLE);
+ if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
+ break;
+ }
+}
+
static void kdamond_usleep(unsigned long usecs)
{
if (usecs > 100 * 1000)
- schedule_timeout_interruptible(usecs_to_jiffies(usecs));
+ schedule_timeout_idle(usecs_to_jiffies(usecs));
else
- usleep_range(usecs, usecs + 1);
+ damon_usleep_idle(usecs);
}
/* Returns negative error code if it's not activated but should return */
@@ -1036,7 +1051,7 @@ static int kdamond_fn(void *data)
ctx->callback.after_sampling(ctx))
done = true;
- usleep_range(ctx->sample_interval, ctx->sample_interval + 1);
+ kdamond_usleep(ctx->sample_interval);
if (ctx->primitive.check_accesses)
max_nr_accesses = ctx->primitive.check_accesses(ctx);
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/damon/core: Avoid fake load reports due to uninterruptible sleeps
2021-11-24 14:52 [PATCH] mm/damon/core: Avoid fake load reports due to uninterruptible sleeps SeongJae Park
@ 2021-11-24 21:42 ` Andrew Morton
2021-11-25 7:49 ` SeongJae Park
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2021-11-24 21:42 UTC (permalink / raw)
To: SeongJae Park; +Cc: shakeelb, linux-mm, linux-kernel, stable
On Wed, 24 Nov 2021 14:52:19 +0000 SeongJae Park <sj@kernel.org> wrote:
> Because DAMON sleeps in uninterruptible mode, /proc/loadavg reports fake
> load while DAMON is turned on, though it is doing nothing. This can
> confuse users[1]. To avoid the case, this commit makes DAMON sleeps in
> idle mode.
>
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -12,6 +12,8 @@
> #include <linux/kthread.h>
> #include <linux/mm.h>
> #include <linux/random.h>
> +#include <linux/sched.h>
> +#include <linux/sched/debug.h>
> #include <linux/slab.h>
> #include <linux/string.h>
>
> @@ -976,12 +978,25 @@ static unsigned long damos_wmark_wait_us(struct damos *scheme)
> return 0;
> }
>
> +/* sleep for @usecs in idle mode */
> +static void __sched damon_usleep_idle(unsigned long usecs)
> +{
> + ktime_t exp = ktime_add_us(ktime_get(), usecs);
> + u64 delta = usecs * NSEC_PER_USEC / 100; /* allow 1% error */
> +
> + for (;;) {
> + __set_current_state(TASK_IDLE);
> + if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
> + break;
> + }
> +}
Let's not copy-n-paste usleep_range() into damon code?
A new usleep_idle_range() in kernel/time/timer.c seems like a
worthwhile addition. Perhaps usleep_idle_range() and usleep_range()
can be static inline wrappers against a new, more general function in
kernel/time/timer.c - usleep_range_state(min, max, state)?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/damon/core: Avoid fake load reports due to uninterruptible sleeps
2021-11-24 21:42 ` Andrew Morton
@ 2021-11-25 7:49 ` SeongJae Park
0 siblings, 0 replies; 3+ messages in thread
From: SeongJae Park @ 2021-11-25 7:49 UTC (permalink / raw)
To: Andrew Morton; +Cc: SeongJae Park, shakeelb, linux-mm, linux-kernel, stable
On Wed, 24 Nov 2021 13:42:10 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 24 Nov 2021 14:52:19 +0000 SeongJae Park <sj@kernel.org> wrote:
>
> > Because DAMON sleeps in uninterruptible mode, /proc/loadavg reports fake
> > load while DAMON is turned on, though it is doing nothing. This can
> > confuse users[1]. To avoid the case, this commit makes DAMON sleeps in
> > idle mode.
> >
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -12,6 +12,8 @@
> > #include <linux/kthread.h>
> > #include <linux/mm.h>
> > #include <linux/random.h>
> > +#include <linux/sched.h>
> > +#include <linux/sched/debug.h>
> > #include <linux/slab.h>
> > #include <linux/string.h>
> >
> > @@ -976,12 +978,25 @@ static unsigned long damos_wmark_wait_us(struct damos *scheme)
> > return 0;
> > }
> >
> > +/* sleep for @usecs in idle mode */
> > +static void __sched damon_usleep_idle(unsigned long usecs)
> > +{
> > + ktime_t exp = ktime_add_us(ktime_get(), usecs);
> > + u64 delta = usecs * NSEC_PER_USEC / 100; /* allow 1% error */
> > +
> > + for (;;) {
> > + __set_current_state(TASK_IDLE);
> > + if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
> > + break;
> > + }
> > +}
>
> Let's not copy-n-paste usleep_range() into damon code?
>
> A new usleep_idle_range() in kernel/time/timer.c seems like a
> worthwhile addition. Perhaps usleep_idle_range() and usleep_range()
> can be static inline wrappers against a new, more general function in
> kernel/time/timer.c - usleep_range_state(min, max, state)?
Makes sense, agreed. I will post next version soon.
Thanks,
SJ
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-11-24 14:52 [PATCH] mm/damon/core: Avoid fake load reports due to uninterruptible sleeps SeongJae Park
2021-11-24 21:42 ` Andrew Morton
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