On Thu, Dec 13, 2012 at 04:43:46PM +0100, Michal Hocko wrote:

On Wed 12-12-12 16:43:35, Johannes Weiner wrote:

quoted

In certain cases (kswapd reclaim, memcg target reclaim), a fixed
minimum amount of pages is scanned from the LRU lists on each
iteration, to make progress.

Do not make this minimum bigger than the respective LRU list size,
however, and save some busy work trying to isolate and reclaim pages
that are not there.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Hmm, shrink_lruvec would do:
	nr_to_scan = min_t(unsigned long,
			   nr[lru], SWAP_CLUSTER_MAX);
	nr[lru] -= nr_to_scan;
and isolate_lru_pages does
	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++)
so it shouldn't matter and we shouldn't do any additional loops, right?

Anyway it would be beter if get_scan_count wouldn't ask for more than is
available.

Consider the inactive_list_is_low() check (especially expensive for
memcg anon), lru_add_drain(), lru lock acquisition...

And as I wrote to Mel in the other email, this can happen a lot when
you have memory cgroups in a multi-node environment.

Reviewed-by: Michal Hocko <redacted>

Thanks!

quoted

@@ -1748,15 +1748,17 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 out:
 	for_each_evictable_lru(lru) {
 		int file = is_file_lru(lru);
+		unsigned long size;
 		unsigned long scan;
 
-		scan = get_lru_size(lruvec, lru);
+		size = get_lru_size(lruvec, lru);

+		size = scan = get_lru_size(lruvec, lru);

quoted

 		if (sc->priority || noswap) {
-			scan >>= sc->priority;
+			scan = size >> sc->priority;
 			if (!scan && force_scan)
-				scan = SWAP_CLUSTER_MAX;
+				scan = min(size, SWAP_CLUSTER_MAX);
 			scan = div64_u64(scan * fraction[file], denominator);
-		}
+		} else
+			scan = size;

And this is not necessary then but this is totally nit.

Do you actually find this more readable?  Setting size = scan and then
later scan = size >> sc->priority? :-)

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