On 03/19/2015 09:52 AM, Gioh Kim wrote:
>
>
> 2015-03-19 오후 5:41에 Vlastimil Babka 이(가) 쓴 글:
>> On 03/19/2015 06:30 AM, Gioh Kim wrote:
>>
>> The code below this comment already does the initialization if the cached
>> values
>> are outside zone boundaries (e.g. due to not being initialized). So if I go
>> through what your __reset_isolation_suitable(zone) call possibly fixes:
>>
>> - the code below comment should take care of zone->compact_cached_migrate_pfn
>> and zone->compact_cached_free_pfn.
>> - the value of zone->compact_blockskip_flush shouldn't affect whether
>> compaction
>> is done.
>> - the state of pageblock_skip bits shouldn't matter for compaction via
>> /proc/sys... as that sets ignore_skip_hint = true
>>
>> It might be perhaps possible that the cached scanner positions are close to
>> meeting and compaction occurs but doesn't process much. That would be also
>> true
>> if both were zero, but at least on my x86 system, lowest zone's start_pfn is
>> 1
>> so that would be detected and corrected. Maybe it is zero on yours though?
>> (ARM?).
>
> YES, it is. As comment above, my platform is based on ARM.
Ah, I see.
> zone's start_pfn is 0.
OK, good to know that's possible. In that case it's clear that the proper
initialization doesn't happen, and __compact_finished() decides that scanners
have already met at pfn 0.
>>
>> So in any case, the problem should be identified in more detail so we know
>> the
>> fix is not accidental. It could be also worthwile to always reset scanner
>> positions when doing a /proc triggered compaction, so it's not depending on
>> what
>> happened before.
>>
>
> Excuse my poor english.
> I cannot catch exactly what you want.
> Is this what you want? This resets the position if compaction is started via
> /proc.
Yes that's right, but..
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 8c0d945..827ec06 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1587,8 +1587,10 @@ static void __compact_pgdat(pg_data_t *pgdat, struct
> compact_control *cc)
> INIT_LIST_HEAD(&cc->freepages);
> INIT_LIST_HEAD(&cc->migratepages);
>
> - if (cc->order == -1 || !compaction_deferred(zone, cc->order))
> + if (cc->order == -1 || !compaction_deferred(zone, cc->order))
> {
> + __reset_isolation_suitable(zone);
This will also trigger reset when called from kswapd through compact_pgdat() and
!compaction_deferred() is true.
The reset should be restricted to cc->order == -1 which only happens from /proc
trigger.
> compact_zone(zone, cc);
> + }
>
> if (cc->order > 0) {
> if (zone_watermark_ok(zone, cc->order,
>
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