On 7/21/21 10:18 PM, Andrew Morton wrote: > 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. Acked-by: Vlastimil Babka <vbabka@xxxxxxx> >> >> @@ -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? Yes, thanks. > --- 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; > _ >