[Devel] [PATCH RHEL8 COMMIT] ms/ksm: react on changing "sleep_millisecs" parameter faster

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.34
------>
commit ce155905f103ee3e181a49e80c67ab2f2751de20
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed Jun 2 12:22:06 2021 +0300

    ms/ksm: react on changing "sleep_millisecs" parameter faster
    
    ksm thread unconditionally sleeps in ksm_scan_thread() after each
    iteration:
    
            schedule_timeout_interruptible(
                    msecs_to_jiffies(ksm_thread_sleep_millisecs))
    
    The timeout is configured in /sys/kernel/mm/ksm/sleep_millisecs.
    
    In case of user writes a big value by a mistake, and the thread enters
    into schedule_timeout_interruptible(), it's not possible to cancel the
    sleep by writing a new smaler value; the thread is just sleeping till
    timeout expires.
    
    The patch fixes the problem by waking the thread each time after the value
    is updated.
    
    This also may be useful for debug purposes; and also for userspace
    daemons, which change sleep_millisecs value in dependence of system load.
    
    Link: http://lkml.kernel.org/r/154454107680.3258.3558002210423531566.stgit@localhost.localdomain
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    Acked-by: Cyrill Gorcunov <gorcunov at gmail.com>
    Reviewed-by: Andrew Morton <akpm at linux-foundation.org>
    Cc: Michal Hocko <mhocko at suse.com>
    Cc: Hugh Dickins <hughd at google.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    (cherry-picked from mainstream commit fcf9a0ef8dc3 ("ksm: react on changing "sleep_millisecs" parameter faster"))
    Used ms version instead of vz7 commit c84fa0de2fec ("ms/ksm: React on changing "sleep_millisecs" parameter faster")
    
    Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
 mm/ksm.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 5fec98bee29a..f57c46a24a8b 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -296,6 +296,7 @@ static unsigned long ksm_run = KSM_RUN_STOP;
 static void wait_while_offlining(void);
 
 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
+static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
 static DEFINE_MUTEX(ksm_thread_mutex);
 static DEFINE_SPINLOCK(ksm_mmlist_lock);
 
@@ -2391,6 +2392,8 @@ static int ksmd_should_run(void)
 
 static int ksm_scan_thread(void *nothing)
 {
+	unsigned int sleep_ms;
+
 	set_freezable();
 	set_user_nice(current, 5);
 
@@ -2404,8 +2407,10 @@ static int ksm_scan_thread(void *nothing)
 		try_to_freeze();
 
 		if (ksmd_should_run()) {
-			schedule_timeout_interruptible(
-				msecs_to_jiffies(ksm_thread_sleep_millisecs));
+			sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
+			wait_event_interruptible_timeout(ksm_iter_wait,
+				sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
+				msecs_to_jiffies(sleep_ms));
 		} else {
 			wait_event_freezable(ksm_thread_wait,
 				ksmd_should_run() || kthread_should_stop());
@@ -2825,6 +2830,7 @@ static ssize_t sleep_millisecs_store(struct kobject *kobj,
 		return -EINVAL;
 
 	ksm_thread_sleep_millisecs = msecs;
+	wake_up_interruptible(&ksm_iter_wait);
 
 	return count;
 }