On Wed, 21 Jul 2021 17:43:19 +0530 Charan Teja Reddy <charante@xxxxxxxxxxxxxx> wrote:
> 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.
>
> @@ -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;
I find this comment hard to follow. Is this better?
--- a/mm/compaction.c~mm-compaction-optimize-proactive-compaction-deferrals-fix
+++ a/mm/compaction.c
@@ -2909,11 +2909,11 @@ static int kcompactd(void *p)
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.
+ * Reset the timeout value. The defer timeout from
+ * proactive compaction is lost here but that is fine
+ * as the condition of the zone changing substantionally
+ * then carrying on with the previous defer interval is
+ * not useful.
*/
timeout = default_timeout;
continue;
_
