On Thu, 16 Jun 2016, Ganesh Mahendran wrote:
> diff --git a/mm/compaction.c b/mm/compaction.c
> index fbb7b38..dcfaf57 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1686,12 +1686,16 @@ enum compact_result try_to_compact_pages(gfp_t
> gfp_mask, unsigned int order,
>
> *contended = COMPACT_CONTENDED_NONE;
>
> - /* Check if the GFP flags allow compaction */
> + /*
> + * Check if this is an order-0 request and
> + * if the GFP flags allow compaction.
> + */
This seems obvious.
> if (!order || !may_enter_fs || !may_perform_io)
> return COMPACT_SKIPPED;
>
> trace_mm_compaction_try_to_compact_pages(order, gfp_mask, mode);
>
> + current->flags |= PF_MEMALLOC;
> /* Compact each zone in the list */
> for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
> ac->nodemask) {
> @@ -1768,6 +1772,7 @@ break_loop:
> all_zones_contended = 0;
> break;
> }
> + current->flags &= ~PF_MEMALLOC;
>
> /*
> * If at least one zone wasn't deferred or skipped, we report if all
Compaction don't touch task_struct flags and PF_MEMALLOC is flag used
primarily by the page allocator, moving this to try_to_compact_pages()
doesn't make sense.
You could remove the !order check in try_to_compact_pages(), but I don't
think it offers anything substantial.
