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Subject[PATCH 2/4] swap: Add try_to_unuse_page_entry()
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Add try_to_unuse_page_entry() which can be used to unuse page entries.

This needs try_to_unuse_anon() which is also added, similar to
try_to_unmap_anon().

Originally based on a patch by Nick Piggin from LKML with changes of my
own after hints from Hugh Dickins.

Signed-off-by: Richard Purdie <rpurdie@openedhand.com>

---
include/linux/rmap.h | 6 +++++
include/linux/swap.h | 1
mm/rmap.c | 2 -
mm/swapfile.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 63 insertions(+), 1 deletion(-)

Index: git/mm/swapfile.c
===================================================================
--- git.orig/mm/swapfile.c 2007-01-10 16:44:13.000000000 +0000
+++ git/mm/swapfile.c 2007-01-10 16:53:59.000000000 +0000
@@ -646,6 +646,61 @@ static int unuse_mm(struct mm_struct *mm
return 0;
}

+static int try_to_unuse_anon(swp_entry_t entry, struct page *page)
+{
+ struct anon_vma *anon_vma;
+ struct vm_area_struct *vma;
+
+ anon_vma = page_lock_anon_vma(page);
+ if (!anon_vma)
+ return 0;
+
+ list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+ if (unuse_vma(vma, entry, page))
+ break;
+ }
+ spin_unlock(&anon_vma->lock);
+ return 0;
+}
+
+
+void try_to_unuse_page_entry(struct page *page)
+{
+ struct swap_info_struct *si;
+ unsigned short *swap_map;
+ swp_entry_t entry;
+
+ BUG_ON(!PageLocked(page));
+ BUG_ON(!PageSwapCache(page));
+ BUG_ON(PageWriteback(page));
+ BUG_ON(PagePrivate(page));
+
+ entry.val = page_private(page);
+ si = swap_info_get(entry);
+ if (!si) {
+ WARN_ON(1);
+ return;
+ }
+ swap_map = &si->swap_map[swp_offset(entry)];
+ spin_unlock(&swap_lock);
+
+ BUG_ON(*swap_map == SWAP_MAP_BAD);
+
+ if (!shmem_unuse(entry, page)) {
+ try_to_unuse_anon(entry, page);
+ delete_from_swap_cache(page);
+ } else if (PageSwapCache(page)) {
+ /*
+ * shmem_unuse deleted a swappage from the swap cache, but the
+ * move to filepage failed so it left swappage in cache and
+ * lowered its swap count to pass quickly through the loops in
+ * try_to_unuse(). We must reincrement the count to try again
+ * later (ick).
+ */
+ swap_duplicate(entry);
+ }
+}
+
/*
* Scan swap_map from current position to next entry still in use.
* Recycle to start on reaching the end, returning 0 when empty.
Index: git/include/linux/rmap.h
===================================================================
--- git.orig/include/linux/rmap.h 2007-01-10 16:37:04.000000000 +0000
+++ git/include/linux/rmap.h 2007-01-10 16:48:02.000000000 +0000
@@ -104,6 +104,11 @@ pte_t *page_check_address(struct page *,
unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);

/*
+ * Used by try_to_unuse_anon() and try_to_unmap_anon()
+ */
+struct anon_vma *page_lock_anon_vma(struct page *page);
+
+/*
* Cleans the PTEs of shared mappings.
* (and since clean PTEs should also be readonly, write protects them too)
*
@@ -125,6 +130,7 @@ static inline int page_mkclean(struct pa
return 0;
}

+#define page_lock_anon_vma(page) (0)

#endif /* CONFIG_MMU */

Index: git/mm/rmap.c
===================================================================
--- git.orig/mm/rmap.c 2007-01-10 16:37:04.000000000 +0000
+++ git/mm/rmap.c 2007-01-10 16:48:02.000000000 +0000
@@ -181,7 +181,7 @@ void __init anon_vma_init(void)
* Getting a lock on a stable anon_vma from a page off the LRU is
* tricky: page_lock_anon_vma rely on RCU to guard against the races.
*/
-static struct anon_vma *page_lock_anon_vma(struct page *page)
+struct anon_vma *page_lock_anon_vma(struct page *page)
{
struct anon_vma *anon_vma = NULL;
unsigned long anon_mapping;
Index: git/include/linux/swap.h
===================================================================
--- git.orig/include/linux/swap.h 2007-01-10 16:44:13.000000000 +0000
+++ git/include/linux/swap.h 2007-01-10 16:48:02.000000000 +0000
@@ -252,6 +252,7 @@ extern sector_t swapdev_block(int, pgoff
extern struct swap_info_struct *get_swap_info_struct(unsigned);
extern int can_share_swap_page(struct page *);
extern int remove_exclusive_swap_page(struct page *);
+extern void try_to_unuse_page_entry(struct page *page);
struct backing_dev_info;

extern spinlock_t swap_lock;

-
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