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Subject[PATCH] swap: Use __try_to_reclaim_swap() in free_swap_and_cache()
Date
The code path to reclaim the swap entry in free_swap_and_cache() is
almost same as that of __try_to_reclaim_swap(), the largest difference
is just coding style. So the support to the additional requirement of
free_swap_and_cache() is added into __try_to_reclaim_swap(), and
__try_to_reclaim_swap() is called in free_swap_and_cache() to delete
the duplicated code. This will improve code readability and reduce
the potential bugs.

There are 2 functionality differences between __try_to_reclaim_swap()
and swap entry reclaim code of free_swap_and_cache().

- free_swap_and_cache() only reclaims the swap entry if the page is
unmapped or swap is getting full. The support has been added into
__try_to_reclaim_swap().

- try_to_free_swap() (called by __try_to_reclaim_swap()) checks
pm_suspended_storage(), while free_swap_and_cache() not. I think
this is OK. Because the page and the swap entry can be reclaimed
later eventually.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
---
mm/swapfile.c | 57 +++++++++++++++++++++++++--------------------------------
1 file changed, 25 insertions(+), 32 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 8ee4c93e3316..00bb4ed08410 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -104,26 +104,39 @@ static inline unsigned char swap_count(unsigned char ent)
return ent & ~SWAP_HAS_CACHE; /* may include COUNT_CONTINUED flag */
}

+/* Reclaim the swap entry anyway if possible */
+#define TTRS_ANYWAY 0x1
+/*
+ * Reclaim the swap entry if there are no more mappings of the
+ * corresponding page
+ */
+#define TTRS_UNMAPPED 0x2
+/* Reclaim the swap entry if swap is getting full*/
+#define TTRS_FULL 0x4
+
/* returns 1 if swap entry is freed */
-static int
-__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
+static int __try_to_reclaim_swap(struct swap_info_struct *si,
+ unsigned long offset, unsigned long flags)
{
swp_entry_t entry = swp_entry(si->type, offset);
struct page *page;
int ret = 0;

- page = find_get_page(swap_address_space(entry), swp_offset(entry));
+ page = find_get_page(swap_address_space(entry), offset);
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
+ * When this function is called from scan_swap_map_slots() 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);
+ if ((flags & TTRS_ANYWAY) ||
+ ((flags & TTRS_UNMAPPED) && !page_mapped(page)) ||
+ ((flags & TTRS_FULL) && mem_cgroup_swap_full(page)))
+ ret = try_to_free_swap(page);
unlock_page(page);
}
put_page(page);
@@ -781,7 +794,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
int swap_was_freed;
unlock_cluster(ci);
spin_unlock(&si->lock);
- swap_was_freed = __try_to_reclaim_swap(si, offset);
+ swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
spin_lock(&si->lock);
/* entry was freed successfully, try to use this again */
if (swap_was_freed)
@@ -1680,7 +1693,6 @@ int try_to_free_swap(struct page *page)
int free_swap_and_cache(swp_entry_t entry)
{
struct swap_info_struct *p;
- struct page *page = NULL;
unsigned char count;

if (non_swap_entry(entry))
@@ -1690,31 +1702,12 @@ int free_swap_and_cache(swp_entry_t entry)
if (p) {
count = __swap_entry_free(p, entry, 1);
if (count == SWAP_HAS_CACHE &&
- !swap_page_trans_huge_swapped(p, entry)) {
- page = find_get_page(swap_address_space(entry),
- swp_offset(entry));
- if (page && !trylock_page(page)) {
- put_page(page);
- page = NULL;
- }
- } else if (!count)
+ !swap_page_trans_huge_swapped(p, entry))
+ __try_to_reclaim_swap(p, swp_offset(entry),
+ TTRS_UNMAPPED | TTRS_FULL);
+ else if (!count)
free_swap_slot(entry);
}
- if (page) {
- /*
- * Not mapped elsewhere, or swap space full? Free it!
- * Also recheck PageSwapCache now page is locked (above).
- */
- if (PageSwapCache(page) && !PageWriteback(page) &&
- (!page_mapped(page) || mem_cgroup_swap_full(page)) &&
- !swap_page_trans_huge_swapped(p, entry)) {
- page = compound_head(page);
- delete_from_swap_cache(page);
- SetPageDirty(page);
- }
- unlock_page(page);
- put_page(page);
- }
return p != NULL;
}

--
2.16.4
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