Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 048c27fd authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

[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: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 52b7efdb

mm/swapfile.c

+12 −2
Original line number Diff line number Diff line
@@ -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;