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

[Joonsoo Kim]

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@xxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> ---
>  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? You missed one callsite in
__compact_pgdat().

        if (cc->order == -1)
                __reset_isolation_suitable(zone);

This also needs reset_cached_positions().

Thanks.
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