mirror of https://gitee.com/openkylin/linux.git
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: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir 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: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -79,6 +79,32 @@ static inline unsigned short encode_swapmap(int count, bool has_cache)
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return ret;
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}
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/* returnes 1 if swap entry is freed */
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static int
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__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
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{
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int type = si - swap_info;
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swp_entry_t entry = swp_entry(type, offset);
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struct page *page;
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int ret = 0;
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page = find_get_page(&swapper_space, entry.val);
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if (!page)
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return 0;
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/*
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* This function is called from scan_swap_map() and it's called
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* by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
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* We have to use trylock for avoiding deadlock. This is a special
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* case and you should use try_to_free_swap() with explicit lock_page()
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* in usual operations.
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*/
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if (trylock_page(page)) {
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ret = try_to_free_swap(page);
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unlock_page(page);
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}
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page_cache_release(page);
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return ret;
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}
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/*
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* We need this because the bdev->unplug_fn can sleep and we cannot
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@ -301,6 +327,19 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si,
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goto no_page;
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if (offset > si->highest_bit)
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scan_base = offset = si->lowest_bit;
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/* reuse swap entry of cache-only swap if not busy. */
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if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
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int swap_was_freed;
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spin_unlock(&swap_lock);
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swap_was_freed = __try_to_reclaim_swap(si, offset);
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spin_lock(&swap_lock);
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/* entry was freed successfully, try to use this again */
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if (swap_was_freed)
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goto checks;
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goto scan; /* check next one */
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}
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if (si->swap_map[offset])
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goto scan;
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@ -382,6 +421,10 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si,
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spin_lock(&swap_lock);
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goto checks;
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}
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if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
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spin_lock(&swap_lock);
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goto checks;
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}
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if (unlikely(--latency_ration < 0)) {
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cond_resched();
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latency_ration = LATENCY_LIMIT;
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@ -393,6 +436,10 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si,
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spin_lock(&swap_lock);
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goto checks;
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}
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if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
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spin_lock(&swap_lock);
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goto checks;
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}
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if (unlikely(--latency_ration < 0)) {
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cond_resched();
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latency_ration = LATENCY_LIMIT;
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