[PATCH for-v5.15.x 0/2] mm/damon/core: Fix fake load reports due to uninterruptible sleeps

[PATCH for-v5.15.x 0/2] mm/damon/core: Fix fake load reports due to uninterruptible sleeps

[SeongJae Park]

This patchset is a backport of DAMON fixes that merged in the mainline,
for v5.15.x stable series.

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       | 14 +++++++++++---
 3 files changed, 33 insertions(+), 11 deletions(-)

-- 
2.17.1

[PATCH for-v5.15.x 1/2] timers: implement usleep_idle_range()

[SeongJae Park]

commit e4779015fd5d2fb8390c258268addff24d6077c7 upstream.

Patch series "mm/damon: Fix fake /proc/loadavg reports", v3.

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.

This patch (of 2):

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.

Link: https://lkml.kernel.org/r/20211126145015.15862-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20211126145015.15862-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Cc: John Stultz <john.stultz@linaro.org>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.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 1d0e2ce6b6d9..e8607992c68a 100644
--- a/include/linux/delay.h
+++ b/include/linux/delay.h
@@ -20,6 +20,7 @@
  */
 
 #include <linux/kernel.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 for-v5.15.x 2/2] mm/damon/core: fix fake load reports due to uninterruptible sleeps

[SeongJae Park]

commit 70e9274805fccfd175d0431a947bfd11ee7df40e upstream.

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/

Link: https://lkml.kernel.org/r/20211126145015.15862-3-sj@kernel.org
Fixes: 2224d8485492 ("mm: introduce Data Access MONitor (DAMON)")
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: SeongJae Park <sj@kernel.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/damon/core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 30e9211f494a..7a4912d6e65f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -357,6 +357,15 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
 	return err;
 }
 
+static void kdamond_usleep(unsigned long usecs)
+{
+	/* See Documentation/timers/timers-howto.rst for the thresholds */
+	if (usecs > 20 * 1000)
+		schedule_timeout_idle(usecs_to_jiffies(usecs));
+	else
+		usleep_idle_range(usecs, usecs + 1);
+}
+
 /*
  * __damon_stop() - Stops monitoring of given context.
  * @ctx:	monitoring context
@@ -370,8 +379,7 @@ static int __damon_stop(struct damon_ctx *ctx)
 		ctx->kdamond_stop = true;
 		mutex_unlock(&ctx->kdamond_lock);
 		while (damon_kdamond_running(ctx))
-			usleep_range(ctx->sample_interval,
-					ctx->sample_interval * 2);
+			kdamond_usleep(ctx->sample_interval);
 		return 0;
 	}
 	mutex_unlock(&ctx->kdamond_lock);
@@ -670,7 +678,7 @@ static int kdamond_fn(void *data)
 				ctx->callback.after_sampling(ctx))
 			set_kdamond_stop(ctx);
 
-		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 for-v5.15.x 0/2] mm/damon/core: Fix fake load reports due to uninterruptible sleeps

[Greg KH]

On Sun, Dec 12, 2021 at 08:28:28AM +0000, SeongJae Park wrote:
> This patchset is a backport of DAMON fixes that merged in the mainline,
> for v5.15.x stable series.
> 
> 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       | 14 +++++++++++---
>  3 files changed, 33 insertions(+), 11 deletions(-)
> 
> -- 
> 2.17.1
> 

All now queued up, thanks!

greg k-h