On Fri, Jul 08, 2016 at 10:34:48AM +0100, Mel Gorman wrote: > kswapd scans from highest to lowest for a zone that requires balancing. > This was necessary when reclaim was per-zone to fairly age pages on lower > zones. Now that we are reclaiming on a per-node basis, any eligible zone > can be used and pages will still be aged fairly. This patch avoids > reclaiming excessively unless buffer_heads are over the limit and it's > necessary to reclaim from a higher zone than requested by the waker of > kswapd to relieve low memory pressure. > > [hillf.zj@xxxxxxxxxxxxxxx: Force kswapd reclaim no more than needed] > Link: http://lkml.kernel.org/r/1466518566-30034-12-git-send-email-mgorman@xxxxxxxxxxxxxxxxxxx > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> One and a half observations: > @@ -3144,31 +3144,39 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > > sc.nr_reclaimed = 0; > > - /* Scan from the highest requested zone to dma */ > - for (i = classzone_idx; i >= 0; i--) { > - zone = pgdat->node_zones + i; > - if (!populated_zone(zone)) > - continue; > - > - /* > - * If the number of buffer_heads in the machine > - * exceeds the maximum allowed level and this node > - * has a highmem zone, force kswapd to reclaim from > - * it to relieve lowmem pressure. > - */ > - if (buffer_heads_over_limit && is_highmem_idx(i)) { > - classzone_idx = i; > - break; > - } > + /* > + * If the number of buffer_heads in the machine exceeds the > + * maximum allowed level then reclaim from all zones. This is > + * not specific to highmem as highmem may not exist but it is > + * it is expected that buffer_heads are stripped in writeback. The mention of highmem in this comment make only sense within the context of this diff; it'll be pretty confusing in the standalone code. Also, double "it is" :) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>