From: Christoph Hellwig <hch@lst.de>
Date: Thu, 1 Mar 2018 22:10:31 +0000 (-0800)
Subject: xfs: don't allocate COW blocks for zeroing holes or unwritten extents
X-Git-Tag: v4.16-rc5~24^2~2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=172ed391f6e40f799273e005405041b57c343cf7;p=thirdparty%2Fkernel%2Flinux.git

xfs: don't allocate COW blocks for zeroing holes or unwritten extents

The iomap zeroing interface is smart enough to skip zeroing holes or
unwritten extents.  Don't subvert this logic for reflink files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 66e1edbfb2b2b..4e771e0f11702 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -955,6 +955,13 @@ static inline bool imap_needs_alloc(struct inode *inode,
 		(IS_DAX(inode) && imap->br_state == XFS_EXT_UNWRITTEN);
 }
 
+static inline bool needs_cow_for_zeroing(struct xfs_bmbt_irec *imap, int nimaps)
+{
+	return nimaps &&
+		imap->br_startblock != HOLESTARTBLOCK &&
+		imap->br_state != XFS_EXT_UNWRITTEN;
+}
+
 static inline bool need_excl_ilock(struct xfs_inode *ip, unsigned flags)
 {
 	/*
@@ -1024,7 +1031,9 @@ xfs_file_iomap_begin(
 			goto out_unlock;
 	}
 
-	if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
+	if (xfs_is_reflink_inode(ip) &&
+	    ((flags & IOMAP_WRITE) ||
+	     ((flags & IOMAP_ZERO) && needs_cow_for_zeroing(&imap, nimaps)))) {
 		if (flags & IOMAP_DIRECT) {
 			/*
 			 * A reflinked inode will result in CoW alloc.