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Subject[PATCH 4/4] swap: Simplify shmem_unuse() usage
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Date
Simplify shmem_unuse_inode() removing a confusing optimisation which
requires the caller to call swap_duplicate if the shmem_unuse() call
doesn't succeed.

Based on a patch by Nick Piggin and some of my own changes as discussed
on LKML.

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

---
mm/shmem.c | 12 +++++-------
mm/swapfile.c | 23 ++---------------------
2 files changed, 7 insertions(+), 28 deletions(-)

Index: git/mm/shmem.c
===================================================================
--- git.orig/mm/shmem.c 2007-01-10 16:45:28.000000000 +0000
+++ git/mm/shmem.c 2007-01-10 16:55:59.000000000 +0000
@@ -734,7 +734,7 @@ static int shmem_unuse_inode(struct shme
struct page **dir;
struct page *subdir;
swp_entry_t *ptr;
- int offset;
+ int offset, moved;

idx = 0;
ptr = info->i_direct;
@@ -792,17 +792,15 @@ lost2:
found:
idx += offset;
inode = &info->vfs_inode;
- if (move_from_swap_cache(page, idx, inode->i_mapping) == 0) {
+ moved = (move_from_swap_cache(page, idx, inode->i_mapping) == 0);
+ if (moved) {
info->flags |= SHMEM_PAGEIN;
shmem_swp_set(info, ptr + offset, 0);
}
shmem_swp_unmap(ptr);
spin_unlock(&info->lock);
- /*
- * Decrement swap count even when the entry is left behind:
- * try_to_unuse will skip over mms, then reincrement count.
- */
- swap_free(entry, page);
+ if (moved)
+ swap_free(entry, page);
return 1;
}

Index: git/mm/swapfile.c
===================================================================
--- git.orig/mm/swapfile.c 2007-01-10 16:53:59.000000000 +0000
+++ git/mm/swapfile.c 2007-01-10 16:56:28.000000000 +0000
@@ -689,15 +689,6 @@ void try_to_unuse_page_entry(struct page
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);
}
}

@@ -922,12 +913,6 @@ static int try_to_unuse(unsigned int typ
* read from disk into another page. Splitting into two
* pages would be incorrect if swap supported "shared
* private" pages, but they are handled by tmpfs files.
- *
- * Note shmem_unuse already deleted a swappage from
- * the swap cache, unless the move to filepage failed:
- * in which case it left swappage in cache, lowered its
- * swap count to pass quickly through the loops above,
- * and now we must reincrement count to try again later.
*/
if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
struct writeback_control wbc = {
@@ -938,12 +923,8 @@ static int try_to_unuse(unsigned int typ
lock_page(page);
wait_on_page_writeback(page);
}
- if (PageSwapCache(page)) {
- if (shmem)
- swap_duplicate(entry);
- else
- delete_from_swap_cache(page);
- }
+ if (PageSwapCache(page) && !shmem)
+ delete_from_swap_cache(page);

/*
* So we could skip searching mms once swap count went

-
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