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[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>
This commit is contained in:
Hugh Dickins 2005-09-03 15:54:40 -07:00 committed by Linus Torvalds
parent 52b7efdbe5
commit 048c27fd72
1 changed files with 12 additions and 2 deletions
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14
mm/swapfile.c
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@ -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_dev_info *unused_bdi, struct page *page)
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_map(struct swap_info_struct *si)
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;