mm: vmscan: do not writeback filesystem pages in direct reclaim

[pandora-kernel.git] / mm / vmscan.c

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b1520b0..10f9c59 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -865,6 +865,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                if (PageDirty(page)) {
                        nr_dirty++;
 
+                       /*
+                        * Only kswapd can writeback filesystem pages to
+                        * avoid risk of stack overflow
+                        */
+                       if (page_is_file_cache(page) && !current_is_kswapd()) {
+                               inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP);
+                               goto keep_locked;
+                       }
+
                        if (references == PAGEREF_RECLAIM_CLEAN)
                                goto keep_locked;
                        if (!may_enter_fs)
@@ -1817,12 +1826,19 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
        enum lru_list l;
        int noswap = 0;
        bool force_scan = false;
-       unsigned long nr_force_scan[2];
 
-       /* kswapd does zone balancing and needs to scan this zone */
+       /*
+        * If the zone or memcg is small, nr[l] can be 0.  This
+        * results in no scanning on this priority and a potential
+        * priority drop.  Global direct reclaim can go to the next
+        * zone and tends to have no problems. Global kswapd is for
+        * zone balancing and it needs to scan a minimum amount. When
+        * reclaiming for a memcg, a priority drop can cause high
+        * latencies, so it's better to scan a minimum amount there as
+        * well.
+        */
        if (scanning_global_lru(sc) && current_is_kswapd())
                force_scan = true;
-       /* memcg may have small limit and need to avoid priority drop */
        if (!scanning_global_lru(sc))
                force_scan = true;
 
@@ -1832,8 +1848,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
                fraction[0] = 0;
                fraction[1] = 1;
                denominator = 1;
-               nr_force_scan[0] = 0;
-               nr_force_scan[1] = SWAP_CLUSTER_MAX;
                goto out;
        }
 
@@ -1850,8 +1864,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
                        fraction[0] = 1;
                        fraction[1] = 0;
                        denominator = 1;
-                       nr_force_scan[0] = SWAP_CLUSTER_MAX;
-                       nr_force_scan[1] = 0;
                        goto out;
                }
        }
@@ -1900,11 +1912,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
        fraction[0] = ap;
        fraction[1] = fp;
        denominator = ap + fp + 1;
-       if (force_scan) {
-               unsigned long scan = SWAP_CLUSTER_MAX;
-               nr_force_scan[0] = div64_u64(scan * ap, denominator);
-               nr_force_scan[1] = div64_u64(scan * fp, denominator);
-       }
 out:
        for_each_evictable_lru(l) {
                int file = is_file_lru(l);
@@ -1913,20 +1920,10 @@ out:
                scan = zone_nr_lru_pages(zone, sc, l);
                if (priority || noswap) {
                        scan >>= priority;
+                       if (!scan && force_scan)
+                               scan = SWAP_CLUSTER_MAX;
                        scan = div64_u64(scan * fraction[file], denominator);
                }
-
-               /*
-                * If zone is small or memcg is small, nr[l] can be 0.
-                * This results no-scan on this priority and priority drop down.
-                * For global direct reclaim, it can visit next zone and tend
-                * not to have problems. For global kswapd, it's for zone
-                * balancing and it need to scan a small amounts. When using
-                * memcg, priority drop can cause big latency. So, it's better
-                * to scan small amount. See may_noscan above.
-                */
-               if (!scan && force_scan)
-                       scan = nr_force_scan[file];
                nr[l] = scan;
        }
 }