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Subject[PATCH] vmscan: cleanup the scan batching code
The vmscan batching logic is twisting. Move it into a standalone
function nr_scan_try_batch() and document it. No behavior change.

CC: Nick Piggin <npiggin@suse.de>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/linux/mmzone.h | 4 ++--
mm/page_alloc.c | 2 +-
mm/vmscan.c | 39 ++++++++++++++++++++++++++++-----------
mm/vmstat.c | 8 ++++----
4 files changed, 35 insertions(+), 18 deletions(-)
--- mm.orig/include/linux/mmzone.h
+++ mm/include/linux/mmzone.h
@@ -323,9 +323,9 @@ struct zone {

/* Fields commonly accessed by the page reclaim scanner */
spinlock_t lru_lock;
- struct {
+ struct zone_lru {
struct list_head list;
- unsigned long nr_scan;
+ unsigned long nr_saved_scan; /* accumulated for batching */
} lru[NR_LRU_LISTS];

struct zone_reclaim_stat reclaim_stat;
--- mm.orig/mm/vmscan.c
+++ mm/mm/vmscan.c
@@ -1450,6 +1450,26 @@ static void get_scan_ratio(struct zone *
percent[1] = 100 - percent[0];
}

+/*
+ * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
+ * until we collected @swap_cluster_max pages to scan.
+ */
+static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
+ unsigned long *nr_saved_scan,
+ unsigned long swap_cluster_max)
+{
+ unsigned long nr;
+
+ *nr_saved_scan += nr_to_scan;
+ nr = *nr_saved_scan;
+
+ if (nr >= swap_cluster_max)
+ *nr_saved_scan = 0;
+ else
+ nr = 0;
+
+ return nr;
+}

/*
* This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
@@ -1475,14 +1495,11 @@ static void shrink_zone(int priority, st
scan >>= priority;
scan = (scan * percent[file]) / 100;
}
- if (scanning_global_lru(sc)) {
- zone->lru[l].nr_scan += scan;
- nr[l] = zone->lru[l].nr_scan;
- if (nr[l] >= swap_cluster_max)
- zone->lru[l].nr_scan = 0;
- else
- nr[l] = 0;
- } else
+ if (scanning_global_lru(sc))
+ nr[l] = nr_scan_try_batch(scan,
+ &zone->lru[l].nr_saved_scan,
+ swap_cluster_max);
+ else
nr[l] = scan;
}

@@ -2079,11 +2096,11 @@ static void shrink_all_zones(unsigned lo
l == LRU_ACTIVE_FILE))
continue;

- zone->lru[l].nr_scan += (lru_pages >> prio) + 1;
- if (zone->lru[l].nr_scan >= nr_pages || pass > 3) {
+ zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
+ if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
unsigned long nr_to_scan;

- zone->lru[l].nr_scan = 0;
+ zone->lru[l].nr_saved_scan = 0;
nr_to_scan = min(nr_pages, lru_pages);
nr_reclaimed += shrink_list(l, nr_to_scan, zone,
sc, prio);
--- mm.orig/mm/vmstat.c
+++ mm/mm/vmstat.c
@@ -729,10 +729,10 @@ static void zoneinfo_show_print(struct s
zone->pages_low,
zone->pages_high,
zone->pages_scanned,
- zone->lru[LRU_ACTIVE_ANON].nr_scan,
- zone->lru[LRU_INACTIVE_ANON].nr_scan,
- zone->lru[LRU_ACTIVE_FILE].nr_scan,
- zone->lru[LRU_INACTIVE_FILE].nr_scan,
+ zone->lru[LRU_ACTIVE_ANON].nr_saved_scan,
+ zone->lru[LRU_INACTIVE_ANON].nr_saved_scan,
+ zone->lru[LRU_ACTIVE_FILE].nr_saved_scan,
+ zone->lru[LRU_INACTIVE_FILE].nr_saved_scan,
zone->spanned_pages,
zone->present_pages);

--- mm.orig/mm/page_alloc.c
+++ mm/mm/page_alloc.c
@@ -3544,7 +3544,7 @@ static void __paginginit free_area_init_
zone_pcp_init(zone);
for_each_lru(l) {
INIT_LIST_HEAD(&zone->lru[l].list);
- zone->lru[l].nr_scan = 0;
+ zone->lru[l].nr_saved_scan = 0;
}
zone->reclaim_stat.recent_rotated[0] = 0;
zone->reclaim_stat.recent_rotated[1] = 0;

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