From: Hugh Dickins <hugh@veritas.com>
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>
---
mm/swapfile.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
diff -puN mm/swapfile.c~swap-scan_swap_map-latency-breaks mm/swapfile.c
--- devel/mm/swapfile.c~swap-scan_swap_map-latency-breaks 2005-07-08 22:34:58.000000000 -0700
+++ devel-akpm/mm/swapfile.c 2005-07-08 22:34:58.000000000 -0700
@@ -56,8 +56,6 @@ static DECLARE_MUTEX(swapon_sem);
*/
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 @@ void swap_unplug_io_fn(struct backing_de
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 @@ static inline unsigned long scan_swap_ma
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 @@ checks: if (!(si->flags & SWP_WRITEOK))
swap_device_lock(si);
goto checks;
}
+ if (unlikely(--latency_ration < 0)) {
+ cond_resched();
+ latency_ration = LATENCY_LIMIT;
+ }
}
swap_device_lock(si);
goto lowest;
_