xfs: separate buffer indexing from block map
To support discontiguous buffers in the buffer cache, we need to
separate the cache index variables from the I/O map. While this is
currently a 1:1 mapping, discontiguous buffer support will break
this relationship.
However, for caching purposes, we can still treat them the same as a
contiguous buffer - the block number of the first block and the
length of the buffer - as that is still a unique representation.
Also, the only way we will ever access the discontiguous regions of
buffers is via bulding the complete buffer in the first place, so
using the initial block number and entire buffer length is a sane
way to index the buffers.
Add a block mapping vector construct to the xfs_buf and use it in
the places where we are doing IO instead of the current
b_bn/b_length variables.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 7f1d139..c9c2ba9 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -58,6 +58,7 @@
#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
#define _XBF_KMEM (1 << 21)/* backed by heap memory */
#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */
+#define _XBF_COMPOUND (1 << 23)/* compound buffer */
typedef unsigned int xfs_buf_flags_t;
@@ -75,7 +76,8 @@
{ XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\
{ _XBF_PAGES, "PAGES" }, \
{ _XBF_KMEM, "KMEM" }, \
- { _XBF_DELWRI_Q, "DELWRI_Q" }
+ { _XBF_DELWRI_Q, "DELWRI_Q" }, \
+ { _XBF_COMPOUND, "COMPOUND" }
typedef struct xfs_buftarg {
dev_t bt_dev;
@@ -98,6 +100,11 @@
#define XB_PAGES 2
+struct xfs_buf_map {
+ xfs_daddr_t bm_bn; /* block number for I/O */
+ int bm_len; /* size of I/O */
+};
+
typedef struct xfs_buf {
/*
* first cacheline holds all the fields needed for an uncontended cache
@@ -107,7 +114,7 @@
* fast-path on locking.
*/
struct rb_node b_rbnode; /* rbtree node */
- xfs_daddr_t b_bn; /* block number for I/O */
+ xfs_daddr_t b_bn; /* block number of buffer */
int b_length; /* size of buffer in BBs */
atomic_t b_hold; /* reference count */
atomic_t b_lru_ref; /* lru reclaim ref count */
@@ -127,12 +134,14 @@
struct xfs_trans *b_transp;
struct page **b_pages; /* array of page pointers */
struct page *b_page_array[XB_PAGES]; /* inline pages */
+ struct xfs_buf_map b_map; /* compound buffer map */
int b_io_length; /* IO size in BBs */
atomic_t b_pin_count; /* pin count */
atomic_t b_io_remaining; /* #outstanding I/O requests */
unsigned int b_page_count; /* size of page array */
unsigned int b_offset; /* page offset in first page */
unsigned short b_error; /* error code on I/O */
+
#ifdef XFS_BUF_LOCK_TRACKING
int b_last_holder;
#endif
@@ -233,8 +242,18 @@
#define XFS_BUF_UNWRITE(bp) ((bp)->b_flags &= ~XBF_WRITE)
#define XFS_BUF_ISWRITE(bp) ((bp)->b_flags & XBF_WRITE)
-#define XFS_BUF_ADDR(bp) ((bp)->b_bn)
-#define XFS_BUF_SET_ADDR(bp, bno) ((bp)->b_bn = (xfs_daddr_t)(bno))
+/*
+ * These macros use the IO block map rather than b_bn. b_bn is now really
+ * just for the buffer cache index for cached buffers. As IO does not use b_bn
+ * anymore, uncached buffers do not use b_bn at all and hence must modify the IO
+ * map directly. Uncached buffers are not allowed to be discontiguous, so this
+ * is safe to do.
+ *
+ * In future, uncached buffers will pass the block number directly to the io
+ * request function and hence these macros will go away at that point.
+ */
+#define XFS_BUF_ADDR(bp) ((bp)->b_map.bm_bn)
+#define XFS_BUF_SET_ADDR(bp, bno) ((bp)->b_map.bm_bn = (xfs_daddr_t)(bno))
static inline void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
{