tmpfs: open a window in shmem_unuse_inode

There are a couple of reasons (patches follow) why it would be good to open a
window for sleep in shmem_unuse_inode, between its search for a matching swap
entry, and its handling of the entry found.

shmem_unuse_inode must then use igrab to hold the inode against deletion in
that window, and its corresponding iput might result in deletion: so it had
better unlock_page before the iput, and might as well release the page too.

Nor is there any need to hold on to shmem_swaplist_mutex once we know we'll
leave the loop.  So this unwinding moves from try_to_unuse and shmem_unuse
into shmem_unuse_inode, in the case when it finds a match.

Let try_to_unuse break on error in the shmem_unuse case, as it does in the
unuse_mm case: though at this point in the series, no error to break on.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 13 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 14bc4f2..eade24d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -814,7 +814,7 @@ static int try_to_unuse(unsigned int type)
 			atomic_inc(&new_start_mm->mm_users);
 			atomic_inc(&prev_mm->mm_users);
 			spin_lock(&mmlist_lock);
-			while (*swap_map > 1 && !retval &&
+			while (*swap_map > 1 && !retval && !shmem &&
 					(p = p->next) != &start_mm->mmlist) {
 				mm = list_entry(p, struct mm_struct, mmlist);
 				if (!atomic_inc_not_zero(&mm->mm_users))
@@ -846,6 +846,13 @@ static int try_to_unuse(unsigned int type)
 			mmput(start_mm);
 			start_mm = new_start_mm;
 		}
+		if (shmem) {
+			/* page has already been unlocked and released */
+			if (shmem > 0)
+				continue;
+			retval = shmem;
+			break;
+		}
 		if (retval) {
 			unlock_page(page);
 			page_cache_release(page);
@@ -884,12 +891,6 @@ static int try_to_unuse(unsigned int type)
 		 * 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 = {
@@ -900,12 +901,8 @@ static int try_to_unuse(unsigned int type)
 			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))
+			delete_from_swap_cache(page);
 
 		/*
 		 * So we could skip searching mms once swap count went