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;
> _
>
