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mm: vmscan: clean up get_scan_count()

Reclaim pressure balance between anon and file pages is calculated
through a tuple of numerators and a shared denominator.

Exceptional cases that want to force-scan anon or file pages configure
the numerators and denominator such that one list is preferred, which is
not necessarily the most obvious way:

    fraction[0] = 1;
    fraction[1] = 0;
    denominator = 1;
    goto out;

Make this easier by making the force-scan cases explicit and use the
fractionals only in case they are calculated from reclaim history.

[akpm@linux-foundation.org: avoid using unintialized_var()]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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commit 9a2651140ef740b3b67ad47ea3d0af75581aacc6 1 parent 11d16c2
@hnaz hnaz authored torvalds committed
Showing with 44 additions and 21 deletions.
  1. +44 −21 mm/vmscan.c
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65 mm/vmscan.c
@@ -1638,6 +1638,13 @@ static int vmscan_swappiness(struct scan_control *sc)
return mem_cgroup_swappiness(sc->target_mem_cgroup);
}
+enum scan_balance {
+ SCAN_EQUAL,
+ SCAN_FRACT,
+ SCAN_ANON,
+ SCAN_FILE,
+};
+
/*
* Determine how aggressively the anon and file LRU lists should be
* scanned. The relative value of each set of LRU lists is determined
@@ -1650,14 +1657,16 @@ static int vmscan_swappiness(struct scan_control *sc)
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
unsigned long *nr)
{
- unsigned long anon, file, free;
+ struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
+ u64 fraction[2];
+ u64 denominator = 0; /* gcc */
+ struct zone *zone = lruvec_zone(lruvec);
unsigned long anon_prio, file_prio;
+ enum scan_balance scan_balance;
+ unsigned long anon, file, free;
+ bool force_scan = false;
unsigned long ap, fp;
- struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
- u64 fraction[2], denominator;
enum lru_list lru;
- bool force_scan = false;
- struct zone *zone = lruvec_zone(lruvec);
/*
* If the zone or memcg is small, nr[l] can be 0. This
@@ -1676,9 +1685,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || (nr_swap_pages <= 0)) {
- fraction[0] = 0;
- fraction[1] = 1;
- denominator = 1;
+ scan_balance = SCAN_FILE;
goto out;
}
@@ -1690,9 +1697,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* too expensive.
*/
if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
- fraction[0] = 0;
- fraction[1] = 1;
- denominator = 1;
+ scan_balance = SCAN_FILE;
goto out;
}
@@ -1702,9 +1707,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* (unless the swappiness setting disagrees with swapping).
*/
if (!sc->priority && vmscan_swappiness(sc)) {
- fraction[0] = 1;
- fraction[1] = 1;
- denominator = 1;
+ scan_balance = SCAN_EQUAL;
goto out;
}
@@ -1722,9 +1725,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
if (global_reclaim(sc)) {
free = zone_page_state(zone, NR_FREE_PAGES);
if (unlikely(file + free <= high_wmark_pages(zone))) {
- fraction[0] = 1;
- fraction[1] = 0;
- denominator = 1;
+ scan_balance = SCAN_ANON;
goto out;
}
}
@@ -1734,12 +1735,12 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* anything from the anonymous working set right now.
*/
if (!inactive_file_is_low(lruvec)) {
- fraction[0] = 0;
- fraction[1] = 1;
- denominator = 1;
+ scan_balance = SCAN_FILE;
goto out;
}
+ scan_balance = SCAN_FRACT;
+
/*
* With swappiness at 100, anonymous and file have the same priority.
* This scanning priority is essentially the inverse of IO cost.
@@ -1792,9 +1793,31 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
size = get_lru_size(lruvec, lru);
scan = size >> sc->priority;
+
if (!scan && force_scan)
scan = min(size, SWAP_CLUSTER_MAX);
- scan = div64_u64(scan * fraction[file], denominator);
+
+ switch (scan_balance) {
+ case SCAN_EQUAL:
+ /* Scan lists relative to size */
+ break;
+ case SCAN_FRACT:
+ /*
+ * Scan types proportional to swappiness and
+ * their relative recent reclaim efficiency.
+ */
+ scan = div64_u64(scan * fraction[file], denominator);
+ break;
+ case SCAN_FILE:
+ case SCAN_ANON:
+ /* Scan one type exclusively */
+ if ((scan_balance == SCAN_FILE) != file)
+ scan = 0;
+ break;
+ default:
+ /* Look ma, no brain */
+ BUG();
+ }
nr[lru] = scan;
}
}
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