Re: [patch 3/3]vmscan: cleanup kswapd_try_to_sleep
From: KOSAKI Motohiro <hidden>
Date: 2011-08-02 00:35:10
(2011/07/28 17:13), Shaohua Li wrote:
quoted hunk ↗ jump to hunk
cleanup kswapd_try_to_sleep() a little bit. Sometimes kswapd doesn't really sleep. In such case, don't call prepare_to_wait/finish_wait. It just wastes CPU. Signed-off-by: Shaohua Li <redacted> --- mm/vmscan.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) Index: linux/mm/vmscan.c ===================================================================--- linux.orig/mm/vmscan.c 2011-07-28 15:52:35.000000000 +0800 +++ linux/mm/vmscan.c 2011-07-28 15:55:56.000000000 +0800@@ -2709,13 +2709,11 @@ static void kswapd_try_to_sleep(pg_data_ if (freezing(current) || kthread_should_stop()) return; - prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); - /* Try to sleep for a short interval */ if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { + prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); remaining = schedule_timeout(HZ/10); finish_wait(&pgdat->kswapd_wait, &wait); - prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); } /*@@ -2734,7 +2732,9 @@ static void kswapd_try_to_sleep(pg_data_ * them before going back to sleep. */ set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); + prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); schedule(); + finish_wait(&pgdat->kswapd_wait, &wait); set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); } else { if (remaining)@@ -2742,7 +2742,6 @@ static void kswapd_try_to_sleep(pg_data_ else count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); } - finish_wait(&pgdat->kswapd_wait, &wait); } /*
Prepare_to_wait/finish_wait basic usage is below. Briefly,
1) prepare_to_wait() is needed to call every sleeping
2) finish_wait is only need to exit sleeping loop
So, 1) moving prepare_to_wait looks pretty good to me. but I doubt the worth
of moving the finish_wait of function last.
-------------------------------------------------------------------------
#define __wait_event(wq, condition) \
do { \
DEFINE_WAIT(__wait); \
\
for (;;) { \
prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
if (condition) \
break; \
schedule(); \
} \
finish_wait(&wq, &__wait); \
} while (0)
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