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mm/damon: Fix fake /proc/loadavg reports

PATCH In review SeongJae Park 3 participants 5 messages Nov 26, 2021 – Nov 27, 2021

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Stable branch Memory management High-resolution timers, timer wheel, clockevents DAMON
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SeongJae Park

author maintainer
#0 lore raw

v3 cover mm/damon: Fix fake /proc/loadavg reports

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/[email protected]/)
- Cc Oleksandr (Oleksandr Natalenko)
- Add 'Suggested-by:' for Andrew Morton on the first patch

From v1
(https://lore.kernel.org/linux-mm/[email protected]/)
- 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(-)
Signature · 1 line
2.17.1
author maintainer
#1 lore raw

PATCH v3 1/2 timers: Implement usleep_idle_range()

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 <[email protected]>
Signed-off-by SeongJae Park <[email protected]>
---
 include/linux/delay.h | 14 +++++++++++++-
 kernel/time/timer.c   | 16 +++++++++-------
 2 files changed, 22 insertions(+), 8 deletions(-)
include/linux/delay.h +13 -1
index 8eacf67eb212..039e7e0c7378 100644
@@ -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)
 {
kernel/time/timer.c +9 -7
index e3d2c23c413d..85f1021ad459 100644
@@ -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);
Signature · 1 line
2.17.1
Reviewed-by on v3 1/2
#2 lore raw

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

Quoted 10 lines · 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 <[email protected]>
Signed-off-by SeongJae Park <[email protected]>

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

Reviewed-by Thomas Gleixner <[email protected]>
author maintainer
#3 lore raw

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

In reply to 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/[email protected]/

Fixes 2224d8485492 ("mm: introduce Data Access MONitor (DAMON)")
Reported-by Oleksandr Natalenko <[email protected]>
Signed-off-by SeongJae Park <[email protected]>
Cc <[email protected]> # 5.15.x
---
 mm/damon/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
mm/damon/core.c +3 -3
index daacd9536c7c..8cd8fddc931e 100644
@@ -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);
Signature · 1 line
2.17.1
Tested-by on the v3 series
#4 lore raw
In reply to SeongJae Park

Hello.

Quoted 22 lines · 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/[email protected]/)
- Cc Oleksandr (Oleksandr Natalenko)
- Add 'Suggested-by:' for Andrew Morton on the first patch

From v1
(https://lore.kernel.org/linux-mm/[email protected]/)
- Avoid copy-and-pasting usleep_delay() in DAMON code (Andrew Morton)

Quoted 8 lines

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 <[email protected]>

Thank you.

Signature · 1 line
Oleksandr Natalenko (post-factum)