[PATCH 2/9] swap: Add try_to_unuse_page_entry()

[Richard Purdie <rpurdie@openedhand.com>]

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: linux/mm/swapfile.c
===================================================================
--- linux.orig/mm/swapfile.c	2007-02-28 18:12:34.000000000 +0000
+++ linux/mm/swapfile.c	2007-02-28 18:13:07.000000000 +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: linux/include/linux/rmap.h
===================================================================
--- linux.orig/include/linux/rmap.h	2007-02-28 18:12:16.000000000 +0000
+++ linux/include/linux/rmap.h	2007-02-28 18:12:41.000000000 +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: linux/mm/rmap.c
===================================================================
--- linux.orig/mm/rmap.c	2007-02-28 18:12:16.000000000 +0000
+++ linux/mm/rmap.c	2007-02-28 18:12:41.000000000 +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: linux/include/linux/swap.h
===================================================================
--- linux.orig/include/linux/swap.h	2007-02-28 18:12:34.000000000 +0000
+++ linux/include/linux/swap.h	2007-02-28 18:13:04.000000000 +0000
@@ -254,6 +254,7 @@ 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;