Commit bcd49e86 authored by Huang Ying's avatar Huang Ying Committed by Linus Torvalds
Browse files

mm/swapfile.c: use __try_to_reclaim_swap() in free_swap_and_cache() 

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().  free_swap_and_cache() is changed to call
__try_to_reclaim_swap(), and 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.

Link: http://lkml.kernel.org/r/20180827075535.17406-2-ying.huang@intel.com


Signed-off-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
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>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 154221c3

mm/swapfile.c

+25 −32
Original line number Diff line number Diff line
@@ -103,25 +103,38 @@ 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)) {

		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);

	}
@@ -780,7 +793,7 @@ checks: 
		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)
@@ -1612,7 +1625,6 @@ 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))
@@ -1622,31 +1634,12 @@ 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;

}

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