1 files changed, 56 insertions, 2 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 793dcd1..191663a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -84,6 +84,18 @@ struct shmem_xattr {
 	char value[0];
 };
 
+/*
+ * shmem_fallocate and shmem_writepage communicate via inode->i_private
+ * (with i_mutex making sure that it has only one user at a time):
+ * we would prefer not to enlarge the shmem inode just for that.
+ */
+struct shmem_falloc {
+	pgoff_t start;		/* start of range currently being fallocated */
+	pgoff_t next;		/* the next page offset to be fallocated */
+	pgoff_t nr_falloced;	/* how many new pages have been fallocated */
+	pgoff_t nr_unswapped;	/* how often writepage refused to swap out */
+};
+
 /* Flag allocation requirements to shmem_getpage */
 enum sgp_type {
 	SGP_READ,	/* don't exceed i_size, don't allocate page */
@@ -791,8 +803,28 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	 * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
 	 * value into swapfile.c, the only way we can correctly account for a
 	 * fallocated page arriving here is now to initialize it and write it.
+	 *
+	 * That's okay for a page already fallocated earlier, but if we have
+	 * not yet completed the fallocation, then (a) we want to keep track
+	 * of this page in case we have to undo it, and (b) it may not be a
+	 * good idea to continue anyway, once we're pushing into swap.  So
+	 * reactivate the page, and let shmem_fallocate() quit when too many.
 	 */
 	if (!PageUptodate(page)) {
+		if (inode->i_private) {
+			struct shmem_falloc *shmem_falloc;
+			spin_lock(&inode->i_lock);
+			shmem_falloc = inode->i_private;
+			if (shmem_falloc &&
+			    index >= shmem_falloc->start &&
+			    index < shmem_falloc->next)
+				shmem_falloc->nr_unswapped++;
+			else
+				shmem_falloc = NULL;
+			spin_unlock(&inode->i_lock);
+			if (shmem_falloc)
+				goto redirty;
+		}
 		clear_highpage(page);
 		flush_dcache_page(page);
 		SetPageUptodate(page);
@@ -1647,6 +1679,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+	struct shmem_falloc shmem_falloc;
 	pgoff_t start, index, end;
 	int error;
 
@@ -1679,6 +1712,14 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 		goto out;
 	}
 
+	shmem_falloc.start = start;
+	shmem_falloc.next  = start;
+	shmem_falloc.nr_falloced = 0;
+	shmem_falloc.nr_unswapped = 0;
+	spin_lock(&inode->i_lock);
+	inode->i_private = &shmem_falloc;
+	spin_unlock(&inode->i_lock);
+
 	for (index = start; index < end; index++) {
 		struct page *page;
 
@@ -1688,6 +1729,8 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 		 */
 		if (signal_pending(current))
 			error = -EINTR;
+		else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
+			error = -ENOMEM;
 		else
 			error = shmem_getpage(inode, index, &page, SGP_FALLOC,
 									NULL);
@@ -1696,10 +1739,18 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 			shmem_undo_range(inode,
 				(loff_t)start << PAGE_CACHE_SHIFT,
 				(loff_t)index << PAGE_CACHE_SHIFT, true);
-			goto ctime;
+			goto undone;
 		}
 
 		/*
+		 * Inform shmem_writepage() how far we have reached.
+		 * No need for lock or barrier: we have the page lock.
+		 */
+		shmem_falloc.next++;
+		if (!PageUptodate(page))
+			shmem_falloc.nr_falloced++;
+
+		/*
 		 * If !PageUptodate, leave it that way so that freeable pages
 		 * can be recognized if we need to rollback on error later.
 		 * But set_page_dirty so that memory pressure will swap rather
@@ -1714,8 +1765,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 
 	if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
 		i_size_write(inode, offset + len);
-ctime:
 	inode->i_ctime = CURRENT_TIME;
+undone:
+	spin_lock(&inode->i_lock);
+	inode->i_private = NULL;
+	spin_unlock(&inode->i_lock);
 out:
 	mutex_unlock(&inode->i_mutex);
 	return error;