Re: [PATCH RFC 10/10] xfs: Allow block allocator to take an alignment hint

John Garry <john.g.garry@xxxxxxxxxx> · Thu, 6 Feb 2025 08:10:24 +0000

On 05/02/2025 19:20, Darrick J. Wong wrote:
On Tue, Feb 04, 2025 at 12:01:27PM +0000, John Garry wrote:
When issuing an atomic write by the CoW method, give the block allocator a
hint to naturally align the data blocks.

This means that we have a better chance to issuing the atomic write via
HW offload next time.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
  fs/xfs/libxfs/xfs_bmap.c | 7 ++++++-
  fs/xfs/libxfs/xfs_bmap.h | 6 +++++-
  fs/xfs/xfs_reflink.c     | 8 ++++++--
  3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 40ad22fb808b..7a3910018dee 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -3454,6 +3454,12 @@ xfs_bmap_compute_alignments(
  		align = xfs_get_cowextsz_hint(ap->ip);
  	else if (ap->datatype & XFS_ALLOC_USERDATA)
  		align = xfs_get_extsz_hint(ap->ip);
+
+	if (align > 1 && ap->flags & XFS_BMAPI_NALIGN)
+		args->alignment = align;
+	else
+		args->alignment = 1;
+
  	if (align) {
  		if (xfs_bmap_extsize_align(mp, &ap->got, &ap->prev, align, 0,
  					ap->eof, 0, ap->conv, &ap->offset,
@@ -3781,7 +3787,6 @@ xfs_bmap_btalloc(
  		.wasdel		= ap->wasdel,
  		.resv		= XFS_AG_RESV_NONE,
  		.datatype	= ap->datatype,
-		.alignment	= 1,
  		.minalignslop	= 0,
  	};
  	xfs_fileoff_t		orig_offset;
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index 4b721d935994..d68b594c3fa2 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -87,6 +87,9 @@ struct xfs_bmalloca {
  /* Do not update the rmap btree.  Used for reconstructing bmbt from rmapbt. */
  #define XFS_BMAPI_NORMAP	(1u << 10)
  
+/* Try to naturally align allocations */
+#define XFS_BMAPI_NALIGN	(1u << 11)
+
  #define XFS_BMAPI_FLAGS \
  	{ XFS_BMAPI_ENTIRE,	"ENTIRE" }, \
  	{ XFS_BMAPI_METADATA,	"METADATA" }, \
@@ -98,7 +101,8 @@ struct xfs_bmalloca {
  	{ XFS_BMAPI_REMAP,	"REMAP" }, \
  	{ XFS_BMAPI_COWFORK,	"COWFORK" }, \
  	{ XFS_BMAPI_NODISCARD,	"NODISCARD" }, \
-	{ XFS_BMAPI_NORMAP,	"NORMAP" }
+	{ XFS_BMAPI_NORMAP,	"NORMAP" },\
+	{ XFS_BMAPI_NALIGN,	"NALIGN" }

Tihs isn't really "naturally" aligned, is it?  It really means "try to
align allocations to the extent size hint", which isn't required to be a
power of two.

Sure, so I would expect that the user will set extsize/cowextsize 
according to the size what we want to do atomics for, and we can align 
to that. I don't think that it makes a difference that either extsize 
isn't mandated to be a power-of-2.

So then I should rename to XFS_BMAPI_EXTSZALIGN or something like that - ok?

Thanks,
John



--D

  
  
  static inline int xfs_bmapi_aflag(int w)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 60c986300faa..198fb5372f10 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -445,6 +445,11 @@ xfs_reflink_fill_cow_hole(
  	int			nimaps;
  	int			error;
  	bool			found;
+	uint32_t		bmapi_flags = XFS_BMAPI_COWFORK |
+					XFS_BMAPI_PREALLOC;
+
+	if (atomic)
+		bmapi_flags |= XFS_BMAPI_NALIGN;
  
  	resaligned = xfs_aligned_fsb_count(imap->br_startoff,
  		imap->br_blockcount, xfs_get_cowextsz_hint(ip));
@@ -478,8 +483,7 @@ xfs_reflink_fill_cow_hole(
  	/* Allocate the entire reservation as unwritten blocks. */
  	nimaps = 1;
  	error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
-			XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, 0, cmap,
-			&nimaps);
+			bmapi_flags, 0, cmap, &nimaps);
  	if (error)
  		goto out_trans_cancel;
  
--
2.31.1










