[PATCH 5/5] block: truncate page cache only when necessary on fallocate

[Dmitry Monakhov]

Signed-off-by: Dmitry Monakhov <dmonak...@openvz.org>
---
 fs/block_dev.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2eca00e..f4b13e1 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -2075,7 +2075,7 @@ static long blkdev_fallocate(struct file *file, int mode, 
loff_t start,
 {
        struct block_device *bdev = I_BDEV(bdev_file_inode(file));
        struct request_queue *q = bdev_get_queue(bdev);
-       struct address_space *mapping;
+       struct address_space *mapping = bdev->bd_inode->i_mapping;
        loff_t end = start + len - 1;
        loff_t isize;
        int error;
@@ -2102,13 +2102,10 @@ static long blkdev_fallocate(struct file *file, int 
mode, loff_t start,
        if ((start | len) & (bdev_logical_block_size(bdev) - 1))
                return -EINVAL;
 
-       /* Invalidate the page cache, including dirty pages. */
-       mapping = bdev->bd_inode->i_mapping;
-       truncate_inode_pages_range(mapping, start, end);
-
        switch (mode) {
        case FALLOC_FL_ZERO_RANGE:
        case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
+               truncate_inode_pages_range(mapping, start, end);
                error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
                                            GFP_KERNEL, false);
                break;
@@ -2116,12 +2113,14 @@ static long blkdev_fallocate(struct file *file, int 
mode, loff_t start,
                /* Only punch if the device can do zeroing discard. */
                if (!blk_queue_discard(q) || !q->limits.discard_zeroes_data)
                        return -EOPNOTSUPP;
+               truncate_inode_pages_range(mapping, start, end);
                error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
                                             GFP_KERNEL, 0);
                break;
        case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | 
FALLOC_FL_NO_HIDE_STALE:
                if (!blk_queue_discard(q))
                        return -EOPNOTSUPP;
+               truncate_inode_pages_range(mapping, start, end);
                error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
                                             GFP_KERNEL, 0);
                break;
-- 
2.9.3