[PATCH v2 3/3] vmscan: implement swap token priority aging

[KOSAKI Motohiro]

While testing for memcg aware swap token, I observed a swap token
was often grabbed an intermittent running process (eg init, auditd)
and they never release a token.

Why?

Some processes (eg init, auditd, audispd) wake up when a process
exiting. And swap token can be get first page-in process when
a process exiting makes no swap token owner. Thus such above
intermittent running process often get a token.

And currently, swap token priority is only decreased at page fault
path. Then, if the process sleep immediately after to grab swap
token, the swap token priority never be decreased. That's obviously
undesirable.

This patch implement very poor (and lightweight) priority aging.
It only be affect to the above corner case and doesn't change swap
tendency workload performance (eg multi process qsbench load)

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 include/trace/events/vmscan.h |   20 +++++++++++++-------
 mm/thrash.c                   |   11 ++++++++++-
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 1798e0c..b2c33bd 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -366,9 +366,10 @@ DEFINE_EVENT_CONDITION(put_swap_token_template, disable_swap_token,

 TRACE_EVENT_CONDITION(update_swap_token_priority,
 	TP_PROTO(struct mm_struct *mm,
-		 unsigned int old_prio),
+		 unsigned int old_prio,
+		 struct mm_struct *swap_token_mm),

-	TP_ARGS(mm, old_prio),
+	TP_ARGS(mm, old_prio, swap_token_mm),

 	TP_CONDITION(mm->token_priority != old_prio),

@@ -376,16 +377,21 @@ TRACE_EVENT_CONDITION(update_swap_token_priority,
 		__field(struct mm_struct*, mm)
 		__field(unsigned int, old_prio)
 		__field(unsigned int, new_prio)
+		__field(struct mm_struct*, swap_token_mm)
+		__field(unsigned int, swap_token_prio)
 	),

 	TP_fast_assign(
-		__entry->mm = mm;
-		__entry->old_prio = old_prio;
-		__entry->new_prio = mm->token_priority;
+		__entry->mm		= mm;
+		__entry->old_prio	= old_prio;
+		__entry->new_prio	= mm->token_priority;
+		__entry->swap_token_mm	= swap_token_mm;
+		__entry->swap_token_prio = swap_token_mm ? swap_token_mm->token_priority : 0;
 	),

-	TP_printk("mm=%p old_prio=%u new_prio=%u",
-		  __entry->mm, __entry->old_prio, __entry->new_prio)
+	TP_printk("mm=%p old_prio=%u new_prio=%u swap_token_mm=%p token_prio=%u",
+		  __entry->mm, __entry->old_prio, __entry->new_prio,
+		  __entry->swap_token_mm, __entry->swap_token_prio)
 );

 #endif /* _TRACE_VMSCAN_H */
diff --git a/mm/thrash.c b/mm/thrash.c
index 14c6c9f..af46d67 100644
--- a/mm/thrash.c
+++ b/mm/thrash.c
@@ -25,10 +25,13 @@

 #include <trace/events/vmscan.h>

+#define TOKEN_AGING_INTERVAL	(0xFF)
+
 static DEFINE_SPINLOCK(swap_token_lock);
 struct mm_struct *swap_token_mm;
 struct mem_cgroup *swap_token_memcg;
 static unsigned int global_faults;
+static unsigned int last_aging;

 void grab_swap_token(struct mm_struct *mm)
 {
@@ -47,6 +50,11 @@ void grab_swap_token(struct mm_struct *mm)
 	if (!swap_token_mm)
 		goto replace_token;

+	if ((global_faults - last_aging) > TOKEN_AGING_INTERVAL) {
+		swap_token_mm->token_priority /= 2;
+		last_aging = global_faults;
+	}
+
 	if (mm == swap_token_mm) {
 		mm->token_priority += 2;
 		goto update_priority;
@@ -64,7 +72,7 @@ void grab_swap_token(struct mm_struct *mm)
 		goto replace_token;

 update_priority:
-	trace_update_swap_token_priority(mm, old_prio);
+	trace_update_swap_token_priority(mm, old_prio, swap_token_mm);

 out:
 	mm->faultstamp = global_faults;
@@ -80,6 +88,7 @@ replace_token:
 	trace_replace_swap_token(swap_token_mm, mm);
 	swap_token_mm = mm;
 	swap_token_memcg = memcg;
+	last_aging = global_faults;
 	goto out;
 }

-- 
1.7.3.1



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