On Mon, Jan 23, 2012 at 08:30:42PM +0800, Hillf Danton wrote:

On Mon, Jan 23, 2012 at 6:47 PM, Johannes Weiner [off-list ref] wrote:

quoted

On Mon, Jan 23, 2012 at 09:55:07AM +0800, Hillf Danton wrote:

quoted

To avoid reduction in performance of reclaimee, checking overreclaim is added
after shrinking lru list, when pages are reclaimed from mem cgroup.

If over reclaim occurs, shrinking remaining lru lists is skipped, and no more
reclaim for reclaim/compaction.

Signed-off-by: Hillf Danton <redacted>
---

--- a/mm/vmscan.c     Mon Jan 23 00:23:10 2012
+++ b/mm/vmscan.c     Mon Jan 23 09:57:20 2012

@@ -2086,6 +2086,7 @@ static void shrink_mem_cgroup_zone(int p
      unsigned long nr_reclaimed, nr_scanned;
      unsigned long nr_to_reclaim = sc->nr_to_reclaim;
      struct blk_plug plug;
+     bool memcg_over_reclaimed = false;

 restart:
      nr_reclaimed = 0;

@@ -2103,6 +2104,11 @@ restart:

                              nr_reclaimed += shrink_list(lru, nr_to_scan,
                                                          mz, sc, priority);
+
+                             memcg_over_reclaimed = !scanning_global_lru(mz)
+                                     && (nr_reclaimed >= nr_to_reclaim);
+                             if (memcg_over_reclaimed)
+                                     goto out;

Since this merge window, scanning_global_lru() is always false when
the memory controller is enabled, i.e. most common configurations and
distribution kernels.

This will with quite likely have bad effects on zone balancing,
pressure balancing between anon/file lru etc, while you haven't shown
that any workloads actually benefit from this.

Hi Johannes

Thanks for your comment, first.

Impact on zone balance and lru-list balance is introduced actually, but I
dont think the patch is totally responsible for the balance mentioned,
because soft limit, embedded in mem cgroup, is setup by users according to
whatever tastes they have.

Though there is room for the patch to be fine tuned in this direction or that,
over reclaim should not be neglected entirely, but be avoided as much as we
could, or users are enforced to set up soft limit with much care not to mess
up zone balance.

Overreclaim is absolutely horrible with soft limits, but I think there
are more direct reasons than checking nr_to_reclaim only after a full
zone scan, for example, soft limit reclaim is invoked on zones that
are totally fine.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>