xfs: create a separate cow extent size hint for the allocator

Create a per-inode extent size allocator hint for copy-on-write.  This
hint is separate from the existing extent size hint so that CoW can
take advantage of the fragmentation-reducing properties of extent size
hints without disabling delalloc for regular writes.

The extent size hint that's fed to the allocator during a copy on
write operation is the greater of the cowextsize and regular extsize
hint.

During reflink, if we're sharing the entire source file to the entire
destination file and the destination file doesn't already have a
cowextsize hint, propagate the source file's cowextsize hint to the
destination file.

Furthermore, zero the bulkstat buffer prior to setting the fields
so that we don't copy kernel memory contents into userspace.

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

1 files changed, 34 insertions, 7 deletions

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index d4707e627a74..8e894118295f 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -238,6 +238,7 @@ __xfs_reflink_reserve_cow(
 	int			nimaps, eof = 0, error = 0;
 	bool			shared = false, trimmed = false;
 	xfs_extnum_t		idx;
+	xfs_extlen_t		align;
 
 	/* Already reserved?  Skip the refcount btree access. */
 	xfs_bmap_search_extents(ip, *offset_fsb, XFS_COW_FORK, &eof, &idx,
@@ -277,6 +278,10 @@ __xfs_reflink_reserve_cow(
 	if (error)
 		goto out_unlock;
 
+	align = xfs_eof_alignment(ip, xfs_get_cowextsz_hint(ip));
+	if (align)
+		end_fsb = roundup_64(end_fsb, align);
+
 retry:
 	error = xfs_bmapi_reserve_delalloc(ip, XFS_COW_FORK, *offset_fsb,
 			end_fsb - *offset_fsb, &got,
@@ -927,18 +932,19 @@ out_error:
 }
 
 /*
- * Update destination inode size, if necessary.
+ * Update destination inode size & cowextsize hint, if necessary.
  */
 STATIC int
 xfs_reflink_update_dest(
 	struct xfs_inode	*dest,
-	xfs_off_t		newlen)
+	xfs_off_t		newlen,
+	xfs_extlen_t		cowextsize)
 {
 	struct xfs_mount	*mp = dest->i_mount;
 	struct xfs_trans	*tp;
 	int			error;
 
-	if (newlen <= i_size_read(VFS_I(dest)))
+	if (newlen <= i_size_read(VFS_I(dest)) && cowextsize == 0)
 		return 0;
 
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
@@ -948,9 +954,17 @@ xfs_reflink_update_dest(
 	xfs_ilock(dest, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
 
-	trace_xfs_reflink_update_inode_size(dest, newlen);
-	i_size_write(VFS_I(dest), newlen);
-	dest->i_d.di_size = newlen;
+	if (newlen > i_size_read(VFS_I(dest))) {
+		trace_xfs_reflink_update_inode_size(dest, newlen);
+		i_size_write(VFS_I(dest), newlen);
+		dest->i_d.di_size = newlen;
+	}
+
+	if (cowextsize) {
+		dest->i_d.di_cowextsize = cowextsize;
+		dest->i_d.di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
+	}
+
 	xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
 
 	error = xfs_trans_commit(tp);
@@ -1270,6 +1284,7 @@ xfs_reflink_remap_range(
 	xfs_fileoff_t		sfsbno, dfsbno;
 	xfs_filblks_t		fsblen;
 	int			error;
+	xfs_extlen_t		cowextsize;
 	bool			is_same;
 
 	if (!xfs_sb_version_hasreflink(&mp->m_sb))
@@ -1330,7 +1345,19 @@ xfs_reflink_remap_range(
 	if (error)
 		goto out_error;
 
-	error = xfs_reflink_update_dest(dest, destoff + len);
+	/*
+	 * Carry the cowextsize hint from src to dest if we're sharing the
+	 * entire source file to the entire destination file, the source file
+	 * has a cowextsize hint, and the destination file does not.
+	 */
+	cowextsize = 0;
+	if (srcoff == 0 && len == i_size_read(VFS_I(src)) &&
+	    (src->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE) &&
+	    destoff == 0 && len >= i_size_read(VFS_I(dest)) &&
+	    !(dest->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE))
+		cowextsize = src->i_d.di_cowextsize;
+
+	error = xfs_reflink_update_dest(dest, destoff + len, cowextsize);
 	if (error)
 		goto out_error;