Re: [PATCH] mm/compaction: fix missed direct_compaction setting for non-direct compaction

[Vlastimil Babka <vbabka@suse.cz>]

On 3/29/19 9:36 AM, Yafang Shao wrote:
> direct_compaction is not initialized for kcompactd or manually triggered
> compaction (via /proc or /sys).

It doesn't need to, this style of initialization does guarantee that any
field not explicitly mentioned is initialized to 0/NULL/false... and
this pattern is used all over the kernel.

> That may cause unexpected behavior in __compact_finished(), so we should
> set direct_compaction to false explicitly for these compactions.

It's not necessary.

> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/compaction.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 98f99f4..ba2b711 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2400,13 +2400,12 @@ static void compact_node(int nid)
>  		.total_free_scanned = 0,
>  		.mode = MIGRATE_SYNC,
>  		.ignore_skip_hint = true,
> +		.direct_compaction = false,
>  		.whole_zone = true,
>  		.gfp_mask = GFP_KERNEL,
>  	};
>  
> -
>  	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
> -
>  		zone = &pgdat->node_zones[zoneid];
>  		if (!populated_zone(zone))
>  			continue;
> @@ -2522,8 +2521,10 @@ static void kcompactd_do_work(pg_data_t *pgdat)
>  		.classzone_idx = pgdat->kcompactd_classzone_idx,
>  		.mode = MIGRATE_SYNC_LIGHT,
>  		.ignore_skip_hint = false,
> +		.direct_compaction = false,
>  		.gfp_mask = GFP_KERNEL,
>  	};
> +
>  	trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
>  							cc.classzone_idx);
>  	count_compact_event(KCOMPACTD_WAKE);
>