Re: [PATCH 3/3] mm/compaction: add an is_via_compact_memory helper function

[Vlastimil Babka <vbabka@suse.cz>]

On 09/16/2015 02:00 PM, Yaowei Bai wrote:
> Introduce is_via_compact_memory helper function indicating compacting
> via /proc/sys/vm/compact_memory to improve readability.

Note that it can also be through single node, i.e.
/sys/devices/system/node/node0/compact

is_manual_compaction() would perhaps be better name

> To catch this situation in __compaction_suitable, use order as parameter
> directly instead of using struct compact_control.

That can be fixed as well. Remove the test from __compaction_suitable(),
and in compact_zone(), do something like:
   ret = is_manual_compaction() ? COMPACT_CONTINUE : compaction_suitable()

I think it's better since it's more explicit, but I understand others 
might feel differently.

> This patch has no functional changes.
>
> Signed-off-by: Yaowei Bai <bywxiaobai@163.com>
> ---
>   mm/compaction.c | 26 ++++++++++++++------------
>   1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index c5c627a..a8e6593 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1197,6 +1197,15 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>   	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
>   }
>
> +/*
> + * order == -1 is expected when compacting via
> + * /proc/sys/vm/compact_memory
> + */
> +static inline bool is_via_compact_memory(int order)
> +{
> +	return order == -1;
> +}
> +
>   static int __compact_finished(struct zone *zone, struct compact_control *cc,
>   			    const int migratetype)
>   {
> @@ -1223,11 +1232,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc,
>   		return COMPACT_COMPLETE;
>   	}
>
> -	/*
> -	 * order == -1 is expected when compacting via
> -	 * /proc/sys/vm/compact_memory
> -	 */
> -	if (cc->order == -1)
> +	if (is_via_compact_memory(cc->order))
>   		return COMPACT_CONTINUE;
>
>   	/* Compaction run is not finished if the watermark is not met */
> @@ -1290,11 +1295,7 @@ static unsigned long __compaction_suitable(struct zone *zone, int order,
>   	int fragindex;
>   	unsigned long watermark;
>
> -	/*
> -	 * order == -1 is expected when compacting via
> -	 * /proc/sys/vm/compact_memory
> -	 */
> -	if (order == -1)
> +	if (is_via_compact_memory(order))
>   		return COMPACT_CONTINUE;
>
>   	watermark = low_wmark_pages(zone);
> @@ -1658,10 +1659,11 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
>   		 * this makes sure we compact the whole zone regardless of
>   		 * cached scanner positions.
>   		 */
> -		if (cc->order == -1)
> +		if (is_via_compact_memory(cc->order))
>   			__reset_isolation_suitable(zone);
>
> -		if (cc->order == -1 || !compaction_deferred(zone, cc->order))
> +		if (is_via_compact_memory(cc->order) ||
> +				!compaction_deferred(zone, cc->order))
>   			compact_zone(zone, cc);
>
>   		if (cc->order > 0) {
>

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