Commit c9e44410 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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mm: reuse unused swap entry if necessary 



Presently we can know a swap entry is just used as SwapCache via swap_map,
without looking up swap cache.

Then, we have a chance to reuse swap-cache-only swap entries in
get_swap_pages().

This patch tries to free swap-cache-only swap entries if swap is not
enough.

Note: We hit following path when swap_cluster code cannot find a free
cluster.  Then, vm_swap_full() is not only condition to allow the kernel
to reclaim unused swap.

Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarBalbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Tested-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 355cfa73

mm/swapfile.c

+47 −0
Original line number Diff line number Diff line
@@ -79,6 +79,32 @@ static inline unsigned short encode_swapmap(int count, bool has_cache) 
	return ret;

}



/* returnes 1 if swap entry is freed */

static int

__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)

{

	int type = si - swap_info;

	swp_entry_t entry = swp_entry(type, offset);

	struct page *page;

	int ret = 0;



	page = find_get_page(&swapper_space, entry.val);

	if (!page)

		return 0;

	/*

	 * This function is called from scan_swap_map() and it's called

	 * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.

	 * We have to use trylock for avoiding deadlock. This is a special

	 * case and you should use try_to_free_swap() with explicit lock_page()

	 * in usual operations.

	 */

	if (trylock_page(page)) {

		ret = try_to_free_swap(page);

		unlock_page(page);

	}

	page_cache_release(page);

	return ret;

}



/*

 * We need this because the bdev->unplug_fn can sleep and we cannot
@@ -301,6 +327,19 @@ checks: 
		goto no_page;

	if (offset > si->highest_bit)

		scan_base = offset = si->lowest_bit;



	/* reuse swap entry of cache-only swap if not busy. */

	if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {

		int swap_was_freed;

		spin_unlock(&swap_lock);

		swap_was_freed = __try_to_reclaim_swap(si, offset);

		spin_lock(&swap_lock);

		/* entry was freed successfully, try to use this again */

		if (swap_was_freed)

			goto checks;

		goto scan; /* check next one */

	}



	if (si->swap_map[offset])

		goto scan;
@@ -382,6 +421,10 @@ scan: 
			spin_lock(&swap_lock);

			goto checks;

		}

		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {

			spin_lock(&swap_lock);

			goto checks;

		}

		if (unlikely(--latency_ration < 0)) {

			cond_resched();

			latency_ration = LATENCY_LIMIT;
@@ -393,6 +436,10 @@ scan: 
			spin_lock(&swap_lock);

			goto checks;

		}

		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {

			spin_lock(&swap_lock);

			goto checks;

		}

		if (unlikely(--latency_ration < 0)) {

			cond_resched();

			latency_ration = LATENCY_LIMIT;

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