[PATCH] swap: scan_swap_map latency breaks
The get_swap_page/scan_swap_map latency can be so bad that even those without
preemption configured deserve relief: periodically cond_resched.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index fdee145..e675ae5 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -56,8 +56,6 @@
*/
static DECLARE_RWSEM(swap_unplug_sem);
-#define SWAPFILE_CLUSTER 256
-
void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
{
swp_entry_t entry;
@@ -84,9 +82,13 @@
up_read(&swap_unplug_sem);
}
+#define SWAPFILE_CLUSTER 256
+#define LATENCY_LIMIT 256
+
static inline unsigned long scan_swap_map(struct swap_info_struct *si)
{
unsigned long offset, last_in_cluster;
+ int latency_ration = LATENCY_LIMIT;
/*
* We try to cluster swap pages by allocating them sequentially
@@ -117,6 +119,10 @@
si->cluster_next = offset-SWAPFILE_CLUSTER-1;
goto cluster;
}
+ if (unlikely(--latency_ration < 0)) {
+ cond_resched();
+ latency_ration = LATENCY_LIMIT;
+ }
}
swap_device_lock(si);
goto lowest;
@@ -153,6 +159,10 @@
swap_device_lock(si);
goto checks;
}
+ if (unlikely(--latency_ration < 0)) {
+ cond_resched();
+ latency_ration = LATENCY_LIMIT;
+ }
}
swap_device_lock(si);
goto lowest;