Re: [PATCH 3/6] mm, compaction: encapsulate resetting cached scanner positions

[Vlastimil Babka <vbabka@suse.cz>]

On 06/16/2015 07:41 AM, Joonsoo Kim wrote:
> On Wed, Jun 10, 2015 at 11:32:31AM +0200, Vlastimil Babka wrote:
>> Resetting the cached compaction scanner positions is now done implicitly in
>> __reset_isolation_suitable() and compact_finished(). Encapsulate the
>> functionality in a new function reset_cached_positions() and call it explicitly
>> where needed.
>> 
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Cc: Mel Gorman <mgorman@suse.de>
>> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>> Cc: Michal Nazarewicz <mina86@mina86.com>
>> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>> Cc: Christoph Lameter <cl@linux.com>
>> Cc: Rik van Riel <riel@redhat.com>
>> Cc: David Rientjes <rientjes@google.com>
>> ---
>>  mm/compaction.c | 22 ++++++++++++++--------
>>  1 file changed, 14 insertions(+), 8 deletions(-)
>> 
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 7e0a814..d334bb3 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -207,6 +207,13 @@ static inline bool isolation_suitable(struct compact_control *cc,
>>  	return !get_pageblock_skip(page);
>>  }
>>  
>> +static void reset_cached_positions(struct zone *zone)
>> +{
>> +	zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
>> +	zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
>> +	zone->compact_cached_free_pfn = zone_end_pfn(zone);
>> +}
>> +
>>  /*
>>   * This function is called to clear all cached information on pageblocks that
>>   * should be skipped for page isolation when the migrate and free page scanner
>> @@ -218,9 +225,6 @@ static void __reset_isolation_suitable(struct zone *zone)
>>  	unsigned long end_pfn = zone_end_pfn(zone);
>>  	unsigned long pfn;
>>  
>> -	zone->compact_cached_migrate_pfn[0] = start_pfn;
>> -	zone->compact_cached_migrate_pfn[1] = start_pfn;
>> -	zone->compact_cached_free_pfn = end_pfn;
>>  	zone->compact_blockskip_flush = false;
> 
> Is there a valid reason not to call reset_cached_positions() in
> __reset_isolation_suitable?

Hm maybe not, except being somewhat implicit again. It might had a stronger
reason in the previous patchset.

> You missed one callsite in
> __compact_pgdat().
> 
>         if (cc->order == -1)
>                 __reset_isolation_suitable(zone);
> 
> This also needs reset_cached_positions().

Ah, good catch. Thanks.

> 
> Thanks.
> 

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