buffer: have alloc_page_buffers() use __GFP_NOFAIL

Instead of adding weird retry logic in that function, utilize
__GFP_NOFAIL to ensure that the vm takes care of handling any
potential retries appropriately. This means we don't have to
call free_more_memory() from here.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bitmap.c

@@ -368,7 +368,7 @@ static int read_page(struct file *file, unsigned long index,
 	pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
 		 (unsigned long long)index << PAGE_SHIFT);
 
-	bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0);
+	bh = alloc_page_buffers(page, 1<<inode->i_blkbits, false);
 	if (!bh) {
 		ret = -ENOMEM;
 		goto out;

fs/buffer.c

@@ -861,16 +861,19 @@ int remove_inode_buffers(struct inode *inode)
  * which may not fail from ordinary buffer allocations.
  */
 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
-		int retry)
+		bool retry)
 {
 	struct buffer_head *bh, *head;
+	gfp_t gfp = GFP_NOFS;
 	long offset;
 
-try_again:
+	if (retry)
+		gfp |= __GFP_NOFAIL;
+
 	head = NULL;
 	offset = PAGE_SIZE;
 	while ((offset -= size) >= 0) {
-		bh = alloc_buffer_head(GFP_NOFS);
+		bh = alloc_buffer_head(gfp);
 		if (!bh)
 			goto no_grow;
 
@@ -896,23 +899,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 		} while (head);
 	}
 
-	/*
-	 * Return failure for non-async IO requests.  Async IO requests
-	 * are not allowed to fail, so we have to wait until buffer heads
-	 * become available.  But we don't want tasks sleeping with 
-	 * partially complete buffers, so all were released above.
-	 */
-	if (!retry)
-		return NULL;
-
-	/* We're _really_ low on memory. Now we just
-	 * wait for old buffer heads to become free due to
-	 * finishing IO.  Since this is an async request and
-	 * the reserve list is empty, we're sure there are 
-	 * async buffer heads in use.
-	 */
-	free_more_memory();
-	goto try_again;
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(alloc_page_buffers);
 
@@ -1021,7 +1008,7 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	/*
 	 * Allocate some buffers for this page
 	 */
-	bh = alloc_page_buffers(page, size, 0);
+	bh = alloc_page_buffers(page, size, false);
 	if (!bh)
 		goto failed;
 
@@ -1575,7 +1562,7 @@ void create_empty_buffers(struct page *page,
 {
 	struct buffer_head *bh, *head, *tail;
 
-	head = alloc_page_buffers(page, blocksize, 1);
+	head = alloc_page_buffers(page, blocksize, true);
 	bh = head;
 	do {
 		bh->b_state |= b_state;
@@ -2638,7 +2625,7 @@ int nobh_write_begin(struct address_space *mapping,
 	 * Be careful: the buffer linked list is a NULL terminated one, rather
 	 * than the circular one we're used to.
 	 */
-	head = alloc_page_buffers(page, blocksize, 0);
+	head = alloc_page_buffers(page, blocksize, false);
 	if (!head) {
 		ret = -ENOMEM;
 		goto out_release;

fs/ntfs/aops.c

@@ -1739,7 +1739,7 @@ void mark_ntfs_record_dirty(struct page *page, const unsigned int ofs) {
 	spin_lock(&mapping->private_lock);
 	if (unlikely(!page_has_buffers(page))) {
 		spin_unlock(&mapping->private_lock);
-		bh = head = alloc_page_buffers(page, bh_size, 1);
+		bh = head = alloc_page_buffers(page, bh_size, true);
 		spin_lock(&mapping->private_lock);
 		if (likely(!page_has_buffers(page))) {
 			struct buffer_head *tail;

fs/ntfs/mft.c

@@ -507,7 +507,7 @@ int ntfs_sync_mft_mirror(ntfs_volume *vol, const unsigned long mft_no,
 	if (unlikely(!page_has_buffers(page))) {
 		struct buffer_head *tail;
 
-		bh = head = alloc_page_buffers(page, blocksize, 1);
+		bh = head = alloc_page_buffers(page, blocksize, true);
 		do {
 			set_buffer_uptodate(bh);
 			tail = bh;

include/linux/buffer_head.h

@@ -156,7 +156,7 @@ void set_bh_page(struct buffer_head *bh,
 		struct page *page, unsigned long offset);
 int try_to_free_buffers(struct page *);
 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
-		int retry);
+		bool retry);
 void create_empty_buffers(struct page *, unsigned long,
 			unsigned long b_state);
 void end_buffer_read_sync(struct buffer_head *bh, int uptodate);