xfs: introduce BMAPI_ZERO for allocating zeroed extents
To enable DAX to do atomic allocation of zeroed extents, we need to
drive the block zeroing deep into the allocator. Because
xfs_bmapi_write() can return merged extents on allocation that were
only partially allocated (i.e. requested range spans allocated and
hole regions, allocation into the hole was contiguous), we cannot
zero the extent returned from xfs_bmapi_write() as that can
overwrite existing data with zeros.
Hence we have to drive the extent zeroing into the allocation code,
prior to where we merge the extents into the BMBT and return the
resultant map. This means we need to propagate this need down to
the xfs_alloc_vextent() and issue the block zeroing at this point.
While this functionality is being introduced for DAX, there is no
reason why it is specific to DAX - we can per-zero blocks during the
allocation transaction on any type of device. It's just slow (and
usually slower than unwritten allocation and conversion) on
traditional block devices so doesn't tend to get used. We can,
however, hook hardware zeroing optimisations via sb_issue_zeroout()
to this operation, so it may be useful in future and hence the
"allocate zeroed blocks" API needs to be implementation neutral.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
index ca1c816..0ecde4d 100644
--- a/fs/xfs/libxfs/xfs_alloc.h
+++ b/fs/xfs/libxfs/xfs_alloc.h
@@ -101,6 +101,7 @@
struct xfs_mount *mp; /* file system mount point */
struct xfs_buf *agbp; /* buffer for a.g. freelist header */
struct xfs_perag *pag; /* per-ag struct for this agno */
+ struct xfs_inode *ip; /* for userdata zeroing method */
xfs_fsblock_t fsbno; /* file system block number */
xfs_agnumber_t agno; /* allocation group number */
xfs_agblock_t agbno; /* allocation group-relative block # */
@@ -120,15 +121,16 @@
char wasdel; /* set if allocation was prev delayed */
char wasfromfl; /* set if allocation is from freelist */
char isfl; /* set if is freelist blocks - !acctg */
- char userdata; /* set if this is user data */
+ char userdata; /* mask defining userdata treatment */
xfs_fsblock_t firstblock; /* io first block allocated */
} xfs_alloc_arg_t;
/*
* Defines for userdata
*/
-#define XFS_ALLOC_USERDATA 1 /* allocation is for user data*/
-#define XFS_ALLOC_INITIAL_USER_DATA 2 /* special case start of file */
+#define XFS_ALLOC_USERDATA (1 << 0)/* allocation is for user data*/
+#define XFS_ALLOC_INITIAL_USER_DATA (1 << 1)/* special case start of file */
+#define XFS_ALLOC_USERDATA_ZERO (1 << 2)/* zero extent on allocation */
xfs_extlen_t xfs_alloc_longest_free_extent(struct xfs_mount *mp,
struct xfs_perag *pag, xfs_extlen_t need);