xfs: allocate delayed extents in CoW fork

Modify the writepage handler to find and convert pending delalloc
extents to real allocations.  Furthermore, when we're doing non-cow
writes to a part of a file that already has a CoW reservation (the
cowextsz hint that we set up in a subsequent patch facilitates this),
promote the write to copy-on-write so that the entire extent can get
written out as a single extent on disk, thereby reducing post-CoW
fragmentation.

Christoph moved the CoW support code in _map_blocks to a separate helper
function, refactored other functions, and reduced the number of CoW fork
lookups, so I merged those changes here to reduce churn.

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

1 files changed, 79 insertions, 18 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 007a520b5ddc..c76d7a603338 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -31,6 +31,7 @@
 #include "xfs_bmap.h"
 #include "xfs_bmap_util.h"
 #include "xfs_bmap_btree.h"
+#include "xfs_reflink.h"
 #include <linux/gfp.h>
 #include <linux/mpage.h>
 #include <linux/pagevec.h>
@@ -341,6 +342,7 @@ xfs_map_blocks(
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -EIO;
 
+	ASSERT(type != XFS_IO_COW);
 	if (type == XFS_IO_UNWRITTEN)
 		bmapi_flags |= XFS_BMAPI_IGSTATE;
 
@@ -355,6 +357,13 @@ xfs_map_blocks(
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);
 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
 				imap, &nimaps, bmapi_flags);
+	/*
+	 * Truncate an overwrite extent if there's a pending CoW
+	 * reservation before the end of this extent.  This forces us
+	 * to come back to writepage to take care of the CoW.
+	 */
+	if (nimaps && type == XFS_IO_OVERWRITE)
+		xfs_reflink_trim_irec_to_next_cow(ip, offset_fsb, imap);
 	xfs_iunlock(ip, XFS_ILOCK_SHARED);
 
 	if (error)
@@ -365,8 +374,7 @@ xfs_map_blocks(
 		error = xfs_iomap_write_allocate(ip, XFS_DATA_FORK, offset,
 				imap);
 		if (!error)
-			trace_xfs_map_blocks_alloc(ip, offset, count, type,
-					imap);
+			trace_xfs_map_blocks_alloc(ip, offset, count, type, imap);
 		return error;
 	}
 
@@ -739,6 +747,56 @@ out_invalidate:
 	return;
 }
 
+static int
+xfs_map_cow(
+	struct xfs_writepage_ctx *wpc,
+	struct inode		*inode,
+	loff_t			offset,
+	unsigned int		*new_type)
+{
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_bmbt_irec	imap;
+	bool			is_cow = false, need_alloc = false;
+	int			error;
+
+	/*
+	 * If we already have a valid COW mapping keep using it.
+	 */
+	if (wpc->io_type == XFS_IO_COW) {
+		wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap, offset);
+		if (wpc->imap_valid) {
+			*new_type = XFS_IO_COW;
+			return 0;
+		}
+	}
+
+	/*
+	 * Else we need to check if there is a COW mapping at this offset.
+	 */
+	xfs_ilock(ip, XFS_ILOCK_SHARED);
+	is_cow = xfs_reflink_find_cow_mapping(ip, offset, &imap, &need_alloc);
+	xfs_iunlock(ip, XFS_ILOCK_SHARED);
+
+	if (!is_cow)
+		return 0;
+
+	/*
+	 * And if the COW mapping has a delayed extent here we need to
+	 * allocate real space for it now.
+	 */
+	if (need_alloc) {
+		error = xfs_iomap_write_allocate(ip, XFS_COW_FORK, offset,
+				&imap);
+		if (error)
+			return error;
+	}
+
+	wpc->io_type = *new_type = XFS_IO_COW;
+	wpc->imap_valid = true;
+	wpc->imap = imap;
+	return 0;
+}
+
 /*
  * We implement an immediate ioend submission policy here to avoid needing to
  * chain multiple ioends and hence nest mempool allocations which can violate
@@ -771,6 +829,7 @@ xfs_writepage_map(
 	int			error = 0;
 	int			count = 0;
 	int			uptodate = 1;
+	unsigned int		new_type;
 
 	bh = head = page_buffers(page);
 	offset = page_offset(page);
@@ -791,22 +850,13 @@ xfs_writepage_map(
 			continue;
 		}
 
-		if (buffer_unwritten(bh)) {
-			if (wpc->io_type != XFS_IO_UNWRITTEN) {
-				wpc->io_type = XFS_IO_UNWRITTEN;
-				wpc->imap_valid = false;
-			}
-		} else if (buffer_delay(bh)) {
-			if (wpc->io_type != XFS_IO_DELALLOC) {
-				wpc->io_type = XFS_IO_DELALLOC;
-				wpc->imap_valid = false;
-			}
-		} else if (buffer_uptodate(bh)) {
-			if (wpc->io_type != XFS_IO_OVERWRITE) {
-				wpc->io_type = XFS_IO_OVERWRITE;
-				wpc->imap_valid = false;
-			}
-		} else {
+		if (buffer_unwritten(bh))
+			new_type = XFS_IO_UNWRITTEN;
+		else if (buffer_delay(bh))
+			new_type = XFS_IO_DELALLOC;
+		else if (buffer_uptodate(bh))
+			new_type = XFS_IO_OVERWRITE;
+		else {
 			if (PageUptodate(page))
 				ASSERT(buffer_mapped(bh));
 			/*
@@ -819,6 +869,17 @@ xfs_writepage_map(
 			continue;
 		}
 
+		if (xfs_is_reflink_inode(XFS_I(inode))) {
+			error = xfs_map_cow(wpc, inode, offset, &new_type);
+			if (error)
+				goto out;
+		}
+
+		if (wpc->io_type != new_type) {
+			wpc->io_type = new_type;
+			wpc->imap_valid = false;
+		}
+
 		if (wpc->imap_valid)
 			wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
 							 offset);