The patch titled
Subject: mm: compaction: optimize proactive compaction deferrals
has been added to the -mm tree. Its filename is
mm-compaction-optimize-proactive-compaction-deferrals.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-optimize-proactive-compaction-deferrals.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-optimize-proactive-compaction-deferrals.patch
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------------------------------------------------------
From: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
Subject: mm: compaction: optimize proactive compaction deferrals
Vlastimil Babka figured out that when fragmentation score didn't go down
across the proactive compaction i.e. when no progress is made, next wake
up for proactive compaction is deferred for 1 << COMPACT_MAX_DEFER_SHIFT,
i.e. 64 times, with each wakeup interval of
HPAGE_FRAG_CHECK_INTERVAL_MSEC(=500). In each of this wakeup, it just
decrement 'proactive_defer' counter and goes sleep i.e. it is getting
woken to just decrement a counter.
The same deferral time can also achieved by simply doing the
HPAGE_FRAG_CHECK_INTERVAL_MSEC << COMPACT_MAX_DEFER_SHIFT thus unnecessary
wakeup of kcompact thread is avoided thus also removes the need of
'proactive_defer' thread counter.
Link: https://lore.kernel.org/linux-fsdevel/88abfdb6-2c13-b5a6-5b46-742d12d1c910@xxxxxxx/
Link: https://lkml.kernel.org/r/1626869599-25412-1-git-send-email-charante@xxxxxxxxxxxxxx
Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Nitin Gupta <nigupta@xxxxxxxxxx>
Cc: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
Cc: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
--- a/mm/compaction.c~mm-compaction-optimize-proactive-compaction-deferrals
+++ a/mm/compaction.c
@@ -2885,7 +2885,8 @@ static int kcompactd(void *p)
{
pg_data_t *pgdat = (pg_data_t *)p;
struct task_struct *tsk = current;
- unsigned int proactive_defer = 0;
+ long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
+ long timeout = default_timeout;
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
@@ -2902,23 +2903,30 @@ 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))) {
+ kcompactd_work_requested(pgdat), timeout)) {
psi_memstall_enter(&pflags);
kcompactd_do_work(pgdat);
psi_memstall_leave(&pflags);
+ /*
+ * Reset the timeout value. The defer timeout by
+ * proactive compaction can effectively lost
+ * here but that is fine as the condition of the
+ * zone changed substantionally and carrying on
+ * with the previous defer is not useful.
+ */
+ timeout = default_timeout;
continue;
}
- /* kcompactd wait timeout */
+ /*
+ * Start the proactive work with default timeout. Based
+ * on the fragmentation score, this timeout is updated.
+ */
+ timeout = default_timeout;
if (should_proactive_compact_node(pgdat)) {
unsigned int prev_score, score;
- if (proactive_defer) {
- proactive_defer--;
- continue;
- }
prev_score = fragmentation_score_node(pgdat);
proactive_compact_node(pgdat);
score = fragmentation_score_node(pgdat);
@@ -2926,8 +2934,9 @@ static int kcompactd(void *p)
* Defer proactive compaction if the fragmentation
* score did not go down i.e. no progress made.
*/
- proactive_defer = score < prev_score ?
- 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
+ if (unlikely(score >= prev_score))
+ timeout =
+ default_timeout << COMPACT_MAX_DEFER_SHIFT;
}
}
_
Patches currently in -mm which might be from charante@xxxxxxxxxxxxxx are
mm-compaction-optimize-proactive-compaction-deferrals.patch
