| Message ID | 20211124145219.32866-1-sj@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/damon/core: Avoid fake load reports due to uninterruptible sleeps | expand |
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)?
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
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);
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(-)