Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for MPOL_PREFERRED_MANY by adding a NO_SLOWPATH gfp bit

On Wed, Mar 10, 2021 at 10:44:11AM +0100, Michal Hocko wrote:

On Wed 10-03-21 13:19:47, Feng Tang wrote:
[...]

quoted

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d66c1c0..00b19f7 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -2205,9 +2205,13 @@ static struct page *alloc_pages_policy(struct mempolicy *pol, gfp_t gfp,
 	 * | MPOL_PREFERRED_MANY (round 2) | local         | NULL       |
 	 * +-------------------------------+---------------+------------+
 	 */
-	if (pol->mode == MPOL_PREFERRED_MANY)
+	if (pol->mode == MPOL_PREFERRED_MANY) {
 		gfp_mask |= __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
 
+		/* Skip direct reclaim, as there will be a second try */
+		gfp_mask &= ~__GFP_DIRECT_RECLAIM;

__GFP_RETRY_MAYFAIL is a reclaim modifier which doesn't make any sense
without __GFP_DIRECT_RECLAIM. Also I think it would be better to have a
proper allocation flags in the initial patch which implements the
fallback.

Ok, will remove the __GFP_RETRY_MAYFAIL setting and folder this with
previous patch(8/14).

Thanks,
Feng

quoted

+	}
+
 	page = __alloc_pages_nodemask(gfp_mask, order,
 				      policy_node(gfp, pol, preferred_nid),
 				      policy_nodemask(gfp, pol));
-- 
2.7.4

-- 
Michal Hocko
SUSE Labs