[PATCH][RFC] mm: Don't put CMA pages on per-cpu lists

[Marek Szyprowski]

Hi Laura,

On Tuesday, June 05, 2012 9:27 PM Laura Abbott wrote:

> Currently, when freeing 0 order pages, CMA pages are treated
> the same as regular movable pages, which means they end up
> on the per-cpu page list. This means that the CMA pages are
> likely to be allocated for something other than contigous
> memory. This increases the chance that the next alloc_contig_range
> will fail because pages can't be migrated.
> 
> Given the size of the CMA region is typically limited, it is best to
> optimize for success of alloc_contig_range as much as possible.
> Do this by freeing CMA pages directly instead of putting them
> on the per-cpu page lists.
> 
> Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
> ---
>  mm/page_alloc.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0e1c6f5..c9a6483 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1310,7 +1310,8 @@ void free_hot_cold_page(struct page *page, int cold)
>  	 * excessively into the page allocator
>  	 */
>  	if (migratetype >= MIGRATE_PCPTYPES) {
> -		if (unlikely(migratetype == MIGRATE_ISOLATE)) {
> +		if (unlikely(migratetype == MIGRATE_ISOLATE)
> +		   || is_migrate_cma(migratetype)) {
>  			free_one_page(zone, page, 0, migratetype);
>  			goto out;
>  		}
> --

Well this patch has some side effects, in some cases it might force kernel to consume regular
movable pages which should be left as a fallback for critical non-movable allocations. Do you
have any statistics for the change introduced by this patch?

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center