[PATCH 05/21] xfs: introduce XFS_BLI_PREALLOC

[Christoph Hellwig <hch@lst.de>]

Add a flag so that the shadow CIL buffer for a buffer log item is always
sizes to the maximum to prevent reallocations.  This will be used for the
RT checksum item, where we know that we are going to fill it up very soon,
and (almost) sequentially, so there is no point in doing a constant
realloc cycle when more data is added to it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_trans_resv.c |  2 +-
 fs/xfs/libxfs/xfs_trans_resv.h |  1 +
 fs/xfs/xfs_buf_item.c          | 10 ++++++++++
 fs/xfs/xfs_buf_item.h          |  4 +++-
 4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index 3151e97ca8ff..5382ece51812 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -53,7 +53,7 @@ xfs_buf_log_overhead(void)
  * will be changed in a transaction.  size is used to tell how many
  * bytes should be reserved per item.
  */
-STATIC uint
+uint
 xfs_calc_buf_res(
 	uint		nbufs,
 	uint		size)
diff --git a/fs/xfs/libxfs/xfs_trans_resv.h b/fs/xfs/libxfs/xfs_trans_resv.h
index 336279e0fc61..1804e821f382 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.h
+++ b/fs/xfs/libxfs/xfs_trans_resv.h
@@ -96,6 +96,7 @@ struct xfs_trans_resv {
 #define	XFS_ITRUNCATE_LOG_COUNT_REFLINK	8
 #define	XFS_WRITE_LOG_COUNT_REFLINK	8
 
+uint xfs_calc_buf_res(uint nbufs, uint size);
 void xfs_trans_resv_calc(struct xfs_mount *mp, struct xfs_trans_resv *resp);
 uint xfs_allocfree_block_count(struct xfs_mount *mp, uint num_ops);
 
diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 1a4ef34af8d5..644c3fb18310 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -252,6 +252,16 @@ xfs_buf_item_size(
 		offset += BBTOB(bp->b_maps[i].bm_len);
 	}
 
+	/*
+	 * For buffers with the prealloc flag, always size the allocation size
+	 * to the maximum as per the log reservation.  This avoids constant
+	 * realloc cycles for buffers that are filled sequentially in rapid
+	 * pace.  Note that the nvecs calaculation is kept from the regular
+	 * look as the buffer item formatting expects it.
+	 */
+	if (bip->bli_flags & XFS_BLI_PREALLOC)
+		*nbytes = xfs_calc_buf_res(bip->bli_format_count, bp->b_length);
+
 	/*
 	 * Round up the buffer size required to minimise the number of memory
 	 * allocations that need to be done as this item grows when relogged by
diff --git a/fs/xfs/xfs_buf_item.h b/fs/xfs/xfs_buf_item.h
index 3159325dd17b..ddc8ecc4683e 100644
--- a/fs/xfs/xfs_buf_item.h
+++ b/fs/xfs/xfs_buf_item.h
@@ -20,6 +20,7 @@ struct xfs_mount;
 #define XFS_BLI_STALE_INODE	(1u << 5)
 #define	XFS_BLI_INODE_BUF	(1u << 6)
 #define	XFS_BLI_ORDERED		(1u << 7)
+#define	XFS_BLI_PREALLOC	(1u << 8)
 
 #define XFS_BLI_FLAGS \
 	{ XFS_BLI_HOLD,		"HOLD" }, \
@@ -29,7 +30,8 @@ struct xfs_mount;
 	{ XFS_BLI_INODE_ALLOC_BUF, "INODE_ALLOC" }, \
 	{ XFS_BLI_STALE_INODE,	"STALE_INODE" }, \
 	{ XFS_BLI_INODE_BUF,	"INODE_BUF" }, \
-	{ XFS_BLI_ORDERED,	"ORDERED" }
+	{ XFS_BLI_ORDERED,	"ORDERED" }, \
+	{ XFS_BLI_PREALLOC,	"PREALLOC" }
 
 /*
  * This is the in core log item structure used to track information
-- 
2.53.0