Commit 210fe530 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
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[PATCH] vmscan: balancing fix

Revert a patch which went into 2.6.8-rc1.  The changelog for that patch was:

  The shrink_zone() logic can, under some circumstances, cause far too many
  pages to be reclaimed.  Say, we're scanning at high priority and suddenly
  hit a large number of reclaimable pages on the LRU.

  Change things so we bale out when SWAP_CLUSTER_MAX pages have been

Problem is, this change caused significant imbalance in inter-zone scan
balancing by truncating scans of larger zones.

Suppose, for example, ZONE_HIGHMEM is 10x the size of ZONE_NORMAL.  The zone
balancing algorithm would require that if we're scanning 100 pages of
ZONE_HIGHMEM, we should scan 10 pages of ZONE_NORMAL.  But this logic will
cause the scanning of ZONE_HIGHMEM to bale out after only 32 pages are
reclaimed.  Thus effectively causing smaller zones to be scanned relatively
harder than large ones.

Now I need to remember what the workload was which caused me to write this
patch originally, then fix it up in a different way...

Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 41e9b63b
......@@ -63,9 +63,6 @@ struct scan_control {
unsigned long nr_mapped; /* From page_state */
/* How many pages shrink_cache() should reclaim */
int nr_to_reclaim;
/* Ask shrink_caches, or shrink_zone to scan at this priority */
unsigned int priority;
......@@ -656,7 +653,6 @@ static void shrink_cache(struct zone *zone, struct scan_control *sc)
if (current_is_kswapd())
mod_page_state(kswapd_steal, nr_freed);
mod_page_state_zone(zone, pgsteal, nr_freed);
sc->nr_to_reclaim -= nr_freed;
......@@ -856,8 +852,6 @@ shrink_zone(struct zone *zone, struct scan_control *sc)
nr_inactive = 0;
sc->nr_to_reclaim = sc->swap_cluster_max;
while (nr_active || nr_inactive) {
if (nr_active) {
sc->nr_to_scan = min(nr_active,
......@@ -871,8 +865,6 @@ shrink_zone(struct zone *zone, struct scan_control *sc)
(unsigned long)sc->swap_cluster_max);
nr_inactive -= sc->nr_to_scan;
shrink_cache(zone, sc);
if (sc->nr_to_reclaim <= 0)
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