[PATCH v3 0/2] mm/damon: Fix fake /proc/loadavg reports

[PATCH v3 0/2] mm/damon: Fix fake /proc/loadavg reports

[SeongJae Park]

This patchset fixes DAMON's fake load report issue.  The first patch
makes yet another variant of usleep_range() for this fix, and the second
patch fixes the issue of DAMON by making it using the newly introduced
function.

I think these need to be applied on v5.15.y, but the second patch 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.  If you think this is not
appropriate for stable tree, please let me know.

Changelog
---------

From v2
(https://lore.kernel.org/linux-mm/20211125160830.30153-1-sj@kernel.org/)
- Cc Oleksandr (Oleksandr Natalenko)
- Add 'Suggested-by:' for Andrew Morton on the first patch

From v1
(https://lore.kernel.org/linux-mm/20211124145219.32866-1-sj@kernel.org/)
- Avoid copy-and-pasting usleep_delay() in DAMON code (Andrew Morton)

SeongJae Park (2):
  timers: Implement usleep_idle_range()
  mm/damon/core: Fix fake load reports due to uninterruptible sleeps

 include/linux/delay.h | 14 +++++++++++++-
 kernel/time/timer.c   | 16 +++++++++-------
 mm/damon/core.c       |  6 +++---
 3 files changed, 25 insertions(+), 11 deletions(-)

-- 
2.17.1

[PATCH v3 1/2] timers: Implement usleep_idle_range()

[SeongJae Park]

Some kernel threads such as DAMON could need to repeatedly sleep in
micro seconds level.  Because usleep_range() sleeps in uninterruptible
state, however, such threads would make /proc/loadavg reports fake load.

To help such cases, this commit implements a variant of usleep_range()
called usleep_idle_range().  It is same to usleep_range() but sets the
state of the current task as TASK_IDLE while sleeping.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/delay.h | 14 +++++++++++++-
 kernel/time/timer.c   | 16 +++++++++-------
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/include/linux/delay.h b/include/linux/delay.h
index 8eacf67eb212..039e7e0c7378 100644
--- a/include/linux/delay.h
+++ b/include/linux/delay.h
@@ -20,6 +20,7 @@
  */
 
 #include <linux/math.h>
+#include <linux/sched.h>
 
 extern unsigned long loops_per_jiffy;
 
@@ -58,7 +59,18 @@ void calibrate_delay(void);
 void __attribute__((weak)) calibration_delay_done(void);
 void msleep(unsigned int msecs);
 unsigned long msleep_interruptible(unsigned int msecs);
-void usleep_range(unsigned long min, unsigned long max);
+void usleep_range_state(unsigned long min, unsigned long max,
+			unsigned int state);
+
+static inline void usleep_range(unsigned long min, unsigned long max)
+{
+	usleep_range_state(min, max, TASK_UNINTERRUPTIBLE);
+}
+
+static inline void usleep_idle_range(unsigned long min, unsigned long max)
+{
+	usleep_range_state(min, max, TASK_IDLE);
+}
 
 static inline void ssleep(unsigned int seconds)
 {
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index e3d2c23c413d..85f1021ad459 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2054,26 +2054,28 @@ unsigned long msleep_interruptible(unsigned int msecs)
 EXPORT_SYMBOL(msleep_interruptible);
 
 /**
- * usleep_range - Sleep for an approximate time
- * @min: Minimum time in usecs to sleep
- * @max: Maximum time in usecs to sleep
+ * usleep_range_state - Sleep for an approximate time in a given state
+ * @min:	Minimum time in usecs to sleep
+ * @max:	Maximum time in usecs to sleep
+ * @state:	State of the current task that will be while sleeping
  *
  * In non-atomic context where the exact wakeup time is flexible, use
- * usleep_range() instead of udelay().  The sleep improves responsiveness
+ * usleep_range_state() instead of udelay().  The sleep improves responsiveness
  * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
  * power usage by allowing hrtimers to take advantage of an already-
  * scheduled interrupt instead of scheduling a new one just for this sleep.
  */
-void __sched usleep_range(unsigned long min, unsigned long max)
+void __sched usleep_range_state(unsigned long min, unsigned long max,
+				unsigned int state)
 {
 	ktime_t exp = ktime_add_us(ktime_get(), min);
 	u64 delta = (u64)(max - min) * NSEC_PER_USEC;
 
 	for (;;) {
-		__set_current_state(TASK_UNINTERRUPTIBLE);
+		__set_current_state(state);
 		/* Do not return before the requested sleep time has elapsed */
 		if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
 			break;
 	}
 }
-EXPORT_SYMBOL(usleep_range);
+EXPORT_SYMBOL(usleep_range_state);
-- 
2.17.1

[PATCH v3 2/2] mm/damon/core: Fix fake load reports due to uninterruptible sleeps

[SeongJae Park]

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
---
 mm/damon/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index daacd9536c7c..8cd8fddc931e 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -979,9 +979,9 @@ static unsigned long damos_wmark_wait_us(struct damos *scheme)
 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);
+		usleep_idle_range(usecs, usecs + 1);
 }
 
 /* Returns negative error code if it's not activated but should return */
@@ -1036,7 +1036,7 @@ 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

Re: [PATCH v3 1/2] timers: Implement usleep_idle_range()

[Thomas Gleixner]

On Fri, Nov 26 2021 at 14:50, SeongJae Park wrote:
> Some kernel threads such as DAMON could need to repeatedly sleep in
> micro seconds level.  Because usleep_range() sleeps in uninterruptible
> state, however, such threads would make /proc/loadavg reports fake load.
>
> To help such cases, this commit implements a variant of usleep_range()
> called usleep_idle_range().  It is same to usleep_range() but sets the
> state of the current task as TASK_IDLE while sleeping.
>
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: SeongJae Park <sj@kernel.org>

Andrew, I assume you want to pick that up along with the mm fix, right?

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Re: [PATCH v3 0/2] mm/damon: Fix fake /proc/loadavg reports

[Oleksandr Natalenko]

Hello.

On pátek 26. listopadu 2021 15:50:13 CET SeongJae Park wrote:
> This patchset fixes DAMON's fake load report issue.  The first patch
> makes yet another variant of usleep_range() for this fix, and the second
> patch fixes the issue of DAMON by making it using the newly introduced
> function.
> 
> I think these need to be applied on v5.15.y, but the second patch 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.  If you think this is not
> appropriate for stable tree, please let me know.
> 
> Changelog
> ---------
> 
> From v2
> (https://lore.kernel.org/linux-mm/20211125160830.30153-1-sj@kernel.org/)
> - Cc Oleksandr (Oleksandr Natalenko)
> - Add 'Suggested-by:' for Andrew Morton on the first patch
> 
> From v1
> (https://lore.kernel.org/linux-mm/20211124145219.32866-1-sj@kernel.org/)
> - Avoid copy-and-pasting usleep_delay() in DAMON code (Andrew Morton)
> 
> SeongJae Park (2):
>   timers: Implement usleep_idle_range()
>   mm/damon/core: Fix fake load reports due to uninterruptible sleeps
> 
>  include/linux/delay.h | 14 +++++++++++++-
>  kernel/time/timer.c   | 16 +++++++++-------
>  mm/damon/core.c       |  6 +++---
>  3 files changed, 25 insertions(+), 11 deletions(-)

For the series:

Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>

Thank you.

-- 
Oleksandr Natalenko (post-factum)