On Sat 11-08-12 01:49:25, KAMEZAWA Hiroyuki wrote:

(2012/08/11 0:42), Michal Hocko wrote:

quoted

On Thu 09-08-12 17:01:10, Glauber Costa wrote:
[...]

quoted

@@ -2317,18 +2318,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	} else
 		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
 	/*
-	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
-	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
-	 *
 	 * Never reclaim on behalf of optional batching, retry with a
 	 * single page instead.
 	 */
-	if (nr_pages == CHARGE_BATCH)
+	if (nr_pages > min_pages)
 		return CHARGE_RETRY;

This is dangerous because THP charges will be retried now while they
previously failed with CHARGE_NOMEM which means that we will keep
attempting potentially endlessly.

with THP, I thought nr_pages == min_pages, and no retry.

right you are.

quoted

Why cannot we simply do if (nr_pages < CHARGE_BATCH) and get rid of the
min_pages altogether?

Hm, I think a slab can be larger than CHARGE_BATCH.

quoted

Also the comment doesn't seem to be valid anymore.

I agree it's not clean. Because our assumption on nr_pages are changed,
I think this behavior should not depend on nr_pages value..
Shouldn't we have a flag to indicate "trial-for-batched charge" ?

dunno, it would require a new parameter anyway (because abusing gfp
doesn't seem great idea).

Thanks,
-Kame




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-- 
Michal Hocko
SUSE Labs