The patch titled
mm: reuse unused swap entry if necessary
has been added to the -mm tree. Its filename is
mm-reuse-unused-swap-entry-if-necessary.patch
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------------------------------------------------------
Subject: mm: reuse unused swap entry if necessary
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Cc: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Dhaval Giani <dhaval@xxxxxxxxxxxxxxxxxx>
Cc: YAMAMOTO Takashi <yamamoto@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff -puN mm/swapfile.c~mm-reuse-unused-swap-entry-if-necessary mm/swapfile.c
--- a/mm/swapfile.c~mm-reuse-unused-swap-entry-if-necessary
+++ a/mm/swapfile.c
@@ -73,6 +73,25 @@ static inline unsigned short make_swap_c
return ret;
}
+static int
+try_to_reuse_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;
+ 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
* hold swap_lock while calling the unplug_fn. And swap_lock
@@ -294,6 +313,18 @@ 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 ret;
+ spin_unlock(&swap_lock);
+ ret = try_to_reuse_swap(si, offset);
+ spin_lock(&swap_lock);
+ if (ret)
+ goto checks; /* we released swap_lock. retry. */
+ goto scan; /* In some racy case */
+ }
+
if (si->swap_map[offset])
goto scan;
@@ -375,6 +406,10 @@ 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;
@@ -386,6 +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;
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
origin.patch
migration-only-migrate_prep-once-per-move_pages.patch
page-allocator-use-integer-fields-lookup-for-gfp_zone-and-check-for-errors-in-flags-passed-to-the-page-allocator.patch
page-allocator-use-integer-fields-lookup-for-gfp_zone-and-check-for-errors-in-flags-passed-to-the-page-allocator-fix-gfp-zone-patch.patch
mm-add-swap-cache-interface-for-swap-reference.patch
mm-modify-swap_map-and-add-swap_has_cache-flag.patch
mm-reuse-unused-swap-entry-if-necessary.patch
memcg-add-file-based-rss-accounting.patch
memcg-add-file-based-rss-accounting-fix-mem_cgroup_update_mapped_file_stat-oops.patch
memcg-remove-mem_cgroup_cache_charge_swapin.patch
memcg-remove-some-redundant-checks.patch
memcg-remove-unneeded-forward-declaration-from-schedh.patch
memcg-fix-swap-accounting.patch
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