mm/damon/core: fix fake load reports due to uninterruptible sleeps

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 30e9211f494a789e04a759464cff667c4f36543d..7a4912d6e65f24e05ae62ff39801d89f8f1493aa 100644 (file)
--- 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);