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mm: vmscan: do not reclaim from kswapd if there is any eligible zone

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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.

[[email protected]: Force kswapd reclaim no more than needed]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Hillf Danton <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Mel Gorman 2016-07-28 15:45:59 -07:00 • committed by Linus Torvalds
commit 86c79f6b54
1 changed files with 27 additions and 32 deletions
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59
mm/vmscan.c
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@ -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 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.
*/
if (buffer_heads_over_limit) {
for (i = MAX_NR_ZONES - 1; 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 (!zone_balanced(zone, order, 0)) {
classzone_idx = i;
break;
}
}
if (i < 0)
goto out;
/*
* Only reclaim if there are no eligible zones. Check from
* high to low zone as allocations prefer higher zones.
* Scanning from low to high zone would allow congestion to be
* cleared during a very small window when a small low
* zone was balanced even under extreme pressure when the
* overall node may be congested.
*/
for (i = classzone_idx; i >= 0; i--) {
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone_balanced(zone, sc.order, classzone_idx))
goto out;
}
/*
* Do some background aging of the anon list, to give
@ -3213,19 +3221,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
if (try_to_freeze() || kthread_should_stop())
break;
/*
* Stop reclaiming if any eligible zone is balanced and clear
* node writeback or congested.
*/
for (i = 0; i <= classzone_idx; i++) {
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone_balanced(zone, sc.order, classzone_idx))
goto out;
}
/*
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages