mm: compaction: proactive compaction trigger by user

The proactive compaction[1] gets triggered for every 500msec and run compaction on the node for COMPACTION_HPAGE_ORDER (usually order-9) pages based on the value set to sysctl.compaction_proactiveness. Triggering the compaction for every 500msec in search of COMPACTION_HPAGE_ORDER pages is not needed for all applications, especially on the embedded system usecases which may have few MB's of RAM. Enabling the proactive compaction in its state will endup in running almost always on such systems.

Other side, proactive compaction can still be very much useful for getting a set of higher order pages in some controllable manner(controlled by using the sysctl.compaction_proactiveness). Thus on systems where enabling the proactive compaction always may proove not required, can trigger the same from user space on write to its sysctl interface. As an example, say app launcher decide to launch the memory heavy application which can be launched fast if it gets more higher order pages thus launcher can prepare the system in advance by triggering the proactive compaction from userspace.

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:
- https://lore.kernel.org/patchwork/patch/1431283/

changes in V1:
- https://lore.kernel.org/lkml/[email protected]/

 Documentation/admin-guide/sysctl/vm.rst |  3 ++-
 include/linux/compaction.h              |  2 ++
 include/linux/mmzone.h                  |  1 +
 kernel/sysctl.c                         |  2 +-
 mm/compaction.c                         | 44 ++++++++++++++++++++++++++++++---
 5 files changed, 47 insertions(+), 5 deletions(-)

Documentation/admin-guide/sysctl/vm.rst +2 -1

index 586cd4b..5e8097d 100644
@@ -126,7 +126,8 @@ compaction_proactiveness
 
 This tunable takes a value in the range [0, 100] with a default value of
 20. This tunable determines how aggressively compaction is done in the
-background. Setting it to 0 disables proactive compaction.
+background. On write of non zero value to this tunable will immediately
+trigger the proactive compaction. Setting it to 0 disables proactive compaction.
 
 Note that compaction has a non-trivial system-wide impact as pages
 belonging to different processes are moved around, which could also lead

include/linux/compaction.h +2 -0

index 4221888..04d5d9f 100644
@@ -84,6 +84,8 @@ static inline unsigned long compact_gap(unsigned int order)
 extern unsigned int sysctl_compaction_proactiveness;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
 			void *buffer, size_t *length, loff_t *ppos);
+extern int compaction_proactiveness_sysctl_handler(struct ctl_table *table,
+		int write, void *buffer, size_t *length, loff_t *ppos);
 extern int sysctl_extfrag_threshold;
 extern int sysctl_compact_unevictable_allowed;
 

include/linux/mmzone.h +1 -0

index 0d53eba..9455809 100644
@@ -815,6 +815,7 @@ typedef struct pglist_data {
 	enum zone_type kcompactd_highest_zoneidx;
 	wait_queue_head_t kcompactd_wait;
 	struct task_struct *kcompactd;
+	bool proactive_compact_trigger;
 #endif
 	/*
 	 * This is a per-node reserve of pages that are not available

kernel/sysctl.c +1 -1

index 14edf84..bed2fad 100644
@@ -2840,7 +2840,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &sysctl_compaction_proactiveness,
 		.maxlen		= sizeof(sysctl_compaction_proactiveness),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= compaction_proactiveness_sysctl_handler,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= &one_hundred,
 	},

mm/compaction.c +41 -3

index 84fde27..197e203 100644
@@ -2708,6 +2708,30 @@ static void compact_nodes(void)
  */
 unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
 
+int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *length, loff_t *ppos)
+{
+	int rc, nid;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
+	if (write && sysctl_compaction_proactiveness) {
+		for_each_online_node(nid) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+
+			if (pgdat->proactive_compact_trigger)
+				continue;
+
+			pgdat->proactive_compact_trigger = true;
+			wake_up_interruptible(&pgdat->kcompactd_wait);
+		}
+	}
+
+	return 0;
+}
+
 /*
  * This is the entry point for compacting all nodes via
  * /proc/sys/vm/compact_memory

@@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
 
 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
 {
-	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
+	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
+		pgdat->proactive_compact_trigger;
 }
 
 static bool kcompactd_node_suitable(pg_data_t *pgdat)

@@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
 		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
 			kcompactd_work_requested(pgdat),
-			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
+			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
+			!pgdat->proactive_compact_trigger) {
 
 			psi_memstall_enter(&pflags);
 			kcompactd_do_work(pgdat);

@@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
 		if (should_proactive_compact_node(pgdat)) {
 			unsigned int prev_score, score;
 
-			if (proactive_defer) {
+			/*
+			 * On wakeup of proactive compaction by sysctl
+			 * write, ignore the accumulated defer score.
+			 * Anyway, if the proactive compaction didn't
+			 * make any progress for the new value, it will
+			 * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
+			 * times.
+			 */
+			if (proactive_defer &&
+				!pgdat->proactive_compact_trigger) {
 				proactive_defer--;
 				continue;
 			}
+
 			prev_score = fragmentation_score_node(pgdat);
 			proactive_compact_node(pgdat);
 			score = fragmentation_score_node(pgdat);

@@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
 			proactive_defer = score < prev_score ?
 					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
 		}
+		if (pgdat->proactive_compact_trigger)
+			pgdat->proactive_compact_trigger = false;
 	}
 
 	return 0;

A gentle ping.

--Charan

Quoted 178 lines · Charan Teja Reddy

The proactive compaction[1] gets triggered for every 500msec and run compaction on the node for COMPACTION_HPAGE_ORDER (usually order-9) pages based on the value set to sysctl.compaction_proactiveness. Triggering the compaction for every 500msec in search of COMPACTION_HPAGE_ORDER pages is not needed for all applications, especially on the embedded system usecases which may have few MB's of RAM. Enabling the proactive compaction in its state will endup in running almost always on such systems.

Other side, proactive compaction can still be very much useful for getting a set of higher order pages in some controllable manner(controlled by using the sysctl.compaction_proactiveness). Thus on systems where enabling the proactive compaction always may proove not required, can trigger the same from user space on write to its sysctl interface. As an example, say app launcher decide to launch the memory heavy application which can be launched fast if it gets more higher order pages thus launcher can prepare the system in advance by triggering the proactive compaction from userspace.

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:
- https://lore.kernel.org/patchwork/patch/1431283/

changes in V1:
- https://lore.kernel.org/lkml/[email protected]/

 Documentation/admin-guide/sysctl/vm.rst |  3 ++-
 include/linux/compaction.h              |  2 ++
 include/linux/mmzone.h                  |  1 +
 kernel/sysctl.c                         |  2 +-
 mm/compaction.c                         | 44 ++++++++++++++++++++++++++++++---
 5 files changed, 47 insertions(+), 5 deletions(-)

Documentation/admin-guide/sysctl/vm.rst +2 -1

index 586cd4b..5e8097d 100644
@@ -126,7 +126,8 @@ compaction_proactiveness
 
 This tunable takes a value in the range [0, 100] with a default value of
 20. This tunable determines how aggressively compaction is done in the
-background. Setting it to 0 disables proactive compaction.
+background. On write of non zero value to this tunable will immediately
+trigger the proactive compaction. Setting it to 0 disables proactive compaction.
 
 Note that compaction has a non-trivial system-wide impact as pages
 belonging to different processes are moved around, which could also lead

include/linux/compaction.h +2 -0

index 4221888..04d5d9f 100644
@@ -84,6 +84,8 @@ static inline unsigned long compact_gap(unsigned int order)
 extern unsigned int sysctl_compaction_proactiveness;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
 			void *buffer, size_t *length, loff_t *ppos);
+extern int compaction_proactiveness_sysctl_handler(struct ctl_table *table,
+		int write, void *buffer, size_t *length, loff_t *ppos);
 extern int sysctl_extfrag_threshold;
 extern int sysctl_compact_unevictable_allowed;
 

include/linux/mmzone.h +1 -0

index 0d53eba..9455809 100644
@@ -815,6 +815,7 @@ typedef struct pglist_data {
 	enum zone_type kcompactd_highest_zoneidx;
 	wait_queue_head_t kcompactd_wait;
 	struct task_struct *kcompactd;
+	bool proactive_compact_trigger;
 #endif
 	/*
 	 * This is a per-node reserve of pages that are not available

kernel/sysctl.c +1 -1

index 14edf84..bed2fad 100644
@@ -2840,7 +2840,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &sysctl_compaction_proactiveness,
 		.maxlen		= sizeof(sysctl_compaction_proactiveness),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= compaction_proactiveness_sysctl_handler,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= &one_hundred,
 	},

mm/compaction.c +41 -3

index 84fde27..197e203 100644
@@ -2708,6 +2708,30 @@ static void compact_nodes(void)
  */
 unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
 
+int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *length, loff_t *ppos)
+{
+	int rc, nid;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
+	if (write && sysctl_compaction_proactiveness) {
+		for_each_online_node(nid) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+
+			if (pgdat->proactive_compact_trigger)
+				continue;
+
+			pgdat->proactive_compact_trigger = true;
+			wake_up_interruptible(&pgdat->kcompactd_wait);
+		}
+	}
+
+	return 0;
+}
+
 /*
  * This is the entry point for compacting all nodes via
  * /proc/sys/vm/compact_memory

@@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
 
 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
 {
-	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
+	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
+		pgdat->proactive_compact_trigger;
 }
 
 static bool kcompactd_node_suitable(pg_data_t *pgdat)

@@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
 		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
 			kcompactd_work_requested(pgdat),
-			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
+			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
+			!pgdat->proactive_compact_trigger) {
 
 			psi_memstall_enter(&pflags);
 			kcompactd_do_work(pgdat);

@@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
 		if (should_proactive_compact_node(pgdat)) {
 			unsigned int prev_score, score;
 
-			if (proactive_defer) {
+			/*
+			 * On wakeup of proactive compaction by sysctl
+			 * write, ignore the accumulated defer score.
+			 * Anyway, if the proactive compaction didn't
+			 * make any progress for the new value, it will
+			 * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
+			 * times.
+			 */
+			if (proactive_defer &&
+				!pgdat->proactive_compact_trigger) {
 				proactive_defer--;
 				continue;
 			}
+
 			prev_score = fragmentation_score_node(pgdat);
 			proactive_compact_node(pgdat);
 			score = fragmentation_score_node(pgdat);

@@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
 			proactive_defer = score < prev_score ?
 					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
 		}
+		if (pgdat->proactive_compact_trigger)
+			pgdat->proactive_compact_trigger = false;
 	}
 
 	return 0;

The proactive compaction[1] gets triggered for every 500msec and run compaction on the node for COMPACTION_HPAGE_ORDER (usually order-9) pages based on the value set to sysctl.compaction_proactiveness. Triggering the compaction for every 500msec in search of COMPACTION_HPAGE_ORDER pages is not needed for all applications, especially on the embedded system usecases which may have few MB's of RAM. Enabling the proactive compaction in its state will endup in running almost always on such systems.

Other side, proactive compaction can still be very much useful for getting a set of higher order pages in some controllable manner(controlled by using the sysctl.compaction_proactiveness). Thus on systems where enabling the proactive compaction always may proove not required, can trigger the same from user space on write to its sysctl interface. As an example, say app launcher decide to launch the memory heavy application which can be launched fast if it gets more higher order pages thus launcher can prepare the system in advance by triggering the proactive compaction from userspace.

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:

*/
unsigned int __read_mostly sysctl_compaction_proactiveness = 20;

mm/compaction.c +7 -0

+int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *length, loff_t *ppos)
+{
+	int rc, nid;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)

mm/compaction.c +24 -3

+			wake_up_interruptible(&pgdat->kcompactd_wait);
+		}
+	}
+
+	return 0;
+}
+
 /*
  * This is the entry point for compacting all nodes via
  * /proc/sys/vm/compact_memory

@@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
 
 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
 {
-	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
+	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
+		pgdat->proactive_compact_trigger;
 }
 
 static bool kcompactd_node_suitable(pg_data_t *pgdat)

@@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
 		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
 			kcompactd_work_requested(pgdat),
-			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
+			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
+			!pgdat->proactive_compact_trigger) {
 
 			psi_memstall_enter(&pflags);
 			kcompactd_do_work(pgdat);

@@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
 		if (should_proactive_compact_node(pgdat)) {
 			unsigned int prev_score, score;
 
-			if (proactive_defer) {
+			/*
+			 * On wakeup of proactive compaction by sysctl
+			 * write, ignore the accumulated defer score.
+			 * Anyway, if the proactive compaction didn't
+			 * make any progress for the new value, it will
+			 * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
+			 * times.
+			 */
+			if (proactive_defer &&
+				!pgdat->proactive_compact_trigger) {
 				proactive_defer--;
 				continue;
 			}
+
 			prev_score = fragmentation_score_node(pgdat);
 			proactive_compact_node(pgdat);
 			score = fragmentation_score_node(pgdat);

@@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
 			proactive_defer = score < prev_score ?
 					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
 		}
+		if (pgdat->proactive_compact_trigger)
+			pgdat->proactive_compact_trigger = false;
 	}
 
 	return 0;

Quoted 8 lines

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:

You forgot to also summarize the changes. Please do in next version.

Quoted 11 lines

*/
unsigned int __read_mostly sysctl_compaction_proactiveness = 20;

mm/compaction.c +7 -0

+int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *length, loff_t *ppos)
+{
+	int rc, nid;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)

mm/compaction.c static void compact_nodes(void) · line 2727

Quoted 10 lines

mm/compaction.c +10 -0

+		return rc;
+
+	if (write && sysctl_compaction_proactiveness) {
+		for_each_online_node(nid) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+
+			if (pgdat->proactive_compact_trigger)
+				continue;
+
+			pgdat->proactive_compact_trigger = true;

I don't like the new variable. I wish we could do without it. I understand this is added to ignore proactive_defer.
We could instead expose proactive_defer in pgdat and reset it to 0 before wakeup (instead being a thread variable in kcompactd). But that would be racy with the

decreases done by kcompactd.
But I like the patch 2/2 and the idea could be extended to proactive_defer handling. If there's no proactive_defer, timeout is HPAGE_FRAG_CHECK_INTERVAL_MSEC. If kcompactd decides to defer, timeout would be HPAGE_FRAG_CHECK_INTERVAL_MSEC << COMPACT_MAX_DEFER_SHIFT. Thus, no more waking up just to decrease proactive_defer, we can then get rid of the counter. On writing new proactiveness just wake up and that's it, regardless of which timeout there was at the moment.

The only change is, if we get woken up to do non-proactive work, by wakeup_kcompactd(), the proactive_defer value would be now be effectively lost. I think it's OK as wakeup_kcompactd() means the condition of the zone changed substantionally anyway and carrying on with previous defer makes not much sense. What do you think?

Quoted 62 lines

mm/compaction.c +24 -3

+			wake_up_interruptible(&pgdat->kcompactd_wait);
+		}
+	}
+
+	return 0;
+}
+
 /*
  * This is the entry point for compacting all nodes via
  * /proc/sys/vm/compact_memory

@@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
 
 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
 {
-	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
+	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
+		pgdat->proactive_compact_trigger;
 }
 
 static bool kcompactd_node_suitable(pg_data_t *pgdat)

@@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
 		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
 			kcompactd_work_requested(pgdat),
-			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
+			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
+			!pgdat->proactive_compact_trigger) {
 
 			psi_memstall_enter(&pflags);
 			kcompactd_do_work(pgdat);

@@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
 		if (should_proactive_compact_node(pgdat)) {
 			unsigned int prev_score, score;
 
-			if (proactive_defer) {
+			/*
+			 * On wakeup of proactive compaction by sysctl
+			 * write, ignore the accumulated defer score.
+			 * Anyway, if the proactive compaction didn't
+			 * make any progress for the new value, it will
+			 * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
+			 * times.
+			 */
+			if (proactive_defer &&
+				!pgdat->proactive_compact_trigger) {
 				proactive_defer--;
 				continue;
 			}
+
 			prev_score = fragmentation_score_node(pgdat);
 			proactive_compact_node(pgdat);
 			score = fragmentation_score_node(pgdat);

@@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
 			proactive_defer = score < prev_score ?
 					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
 		}
+		if (pgdat->proactive_compact_trigger)
+			pgdat->proactive_compact_trigger = false;
 	}
 
 	return 0;

Thanks Vlastimil for your inputs!!

Quoted 9 lines · Vlastimil Babka

Quoted 8 lines

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:

You forgot to also summarize the changes. Please do in next version.

I think we can get rid off 'proactive_defer' thread variable with the timeout approach you suggested. But it is still requires to have one additional variable 'proactive_compact_trigger', which main purpose is to decide if the kcompactd wakeup is for proactive compaction or not. Please see below code:

   if (wait_event_freezable_timeout() && !proactive_compact_trigger) {
	// do the non-proactive work
	continue
   }
   // do the proactive work
     .................

Thus I feel that on writing new proactiveness, it is required to do wakeup_kcomppactd() + set a flag that this wakeup is for proactive work.

Am I failed to get your point here?

Quoted 25 lines · Charan Teja Kalla

Thanks Vlastimil for your inputs!!

Quoted 9 lines · Vlastimil Babka

Quoted 8 lines

This triggering of proactive compaction is done on a write to sysctl.compaction_proactiveness by user.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a

Signed-off-by Charan Teja Reddy <[email protected]>

---
changes in V2:

You forgot to also summarize the changes. Please do in next version.

I think we can get rid off 'proactive_defer' thread variable with the timeout approach you suggested. But it is still requires to have one additional variable 'proactive_compact_trigger', which main purpose is to decide if the kcompactd wakeup is for proactive compaction or not. Please see below code:

   if (wait_event_freezable_timeout() && !proactive_compact_trigger) {
	// do the non-proactive work
	continue
   }
   // do the proactive work
     .................

Quoted 4 lines

Thus I feel that on writing new proactiveness, it is required to do wakeup_kcomppactd() + set a flag that this wakeup is for proactive work.

Am I failed to get your point here?

The check whether to do non-proactive work is already guarded by kcompactd_work_requested(), which looks at pgdat->kcompactd_max_order and this is set by wakeup_kcompactd().

So with a plain wakeup where we don't set pgdat->kcompactd_max_order will make it consider proactive work instead and we don't need another trigger variable AFAICS.

The wait_event/freezable_timeout() documentation says that:
* Returns:
* 0 if the @condition evaluated to %false after the @timeout elapsed, or
* 1 if the @condition evaluated to %true after the @timeout elapsed,
* or the remaining jiffies (at least 1) if the @condition evaluated
* to %true before the @timeout elapsed.

which means the condition must be evaluated to true or timeout should be elapsed for the function wait_event_freezable_timeout() to return.

Please check the macro implementation of __wait_event, where it will be in for(;;) till the condition is evaluated to true or timeout happens. #define __wait_event_freezable_timeout(wq_head, condition, timeout)

___wait_event(wq_head, ___wait_cond_timeout(condition),

TASK_INTERRUPTIBLE, 0, timeout,

__ret = freezable_schedule_timeout(__ret))

Thus the plain wakeup of kcompactd don't do the proactive compact work. And so we should identify its wakeup for proactive work with a separate flag.