xfs: skip online discard during eofblocks trims

We've had reports of online discard operations being sent from XFS
on write-only workloads. These discards occur as a result of
eofblocks trims that can occur after a large file copy completes.

These discards are slightly confusing for users who might be paying
close attention to online discards (i.e., vdo) due to performance
sensitivity. They also happen to be spurious because freed post-eof
blocks by definition have not been written to during the current
allocation cycle.

Update xfs_free_eofblocks() to skip discards that are purely
attributed to eofblocks trims. This cuts down the number of spurious
discards that may occur on write-only workloads due to normal
preallocation activity.

Note that discards of post-eof extents can still occur from other
codepaths that do not isolate handling of post-eof blocks from those
within eof. For example, file unlinks and truncates may still cause
discards for any file blocks affected by the operation.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 8cd8c41..696c3b6 100644 (file)
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -871,8 +871,8 @@ xfs_free_eofblocks(
                 * contents of the file are flushed to disk then the files
                 * may be full of holes (ie NULL files bug).
                 */
-               error = xfs_itruncate_extents(&tp, ip, XFS_DATA_FORK,
-                                             XFS_ISIZE(ip));
+               error = xfs_itruncate_extents_nodiscard(&tp, ip, XFS_DATA_FORK,
+                                                       XFS_ISIZE(ip));
                if (error) {
                        /*
                         * If we get an error at this point we simply don't

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 42781ba..5b2e084 100644 (file)
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1548,11 +1548,12 @@ xfs_itruncate_clear_reflink_flags(
  * dirty on error so that transactions can be easily aborted if possible.
  */
 int
-xfs_itruncate_extents(
+__xfs_itruncate_extents(
        struct xfs_trans        **tpp,
        struct xfs_inode        *ip,
        int                     whichfork,
-       xfs_fsize_t             new_size)
+       xfs_fsize_t             new_size,
+       bool                    skip_discard)
 {
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_trans        *tp = *tpp;
@@ -1563,6 +1564,7 @@ xfs_itruncate_extents(
        xfs_filblks_t           unmap_len;
        int                     error = 0;
        int                     done = 0;
+       int                     flags;
 
        ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
        ASSERT(!atomic_read(&VFS_I(ip)->i_count) ||
@@ -1575,6 +1577,10 @@ xfs_itruncate_extents(
 
        trace_xfs_itruncate_extents_start(ip, new_size);
 
+       flags = xfs_bmapi_aflag(whichfork);
+       if (skip_discard)
+               flags |= XFS_BMAPI_NODISCARD;
+
        /*
         * Since it is possible for space to become allocated beyond
         * the end of the file (in a crash where the space is allocated
@@ -1593,12 +1599,9 @@ xfs_itruncate_extents(
        unmap_len = last_block - first_unmap_block + 1;
        while (!done) {
                xfs_defer_init(&dfops, &first_block);
-               error = xfs_bunmapi(tp, ip,
-                                   first_unmap_block, unmap_len,
-                                   xfs_bmapi_aflag(whichfork),
-                                   XFS_ITRUNC_MAX_EXTENTS,
-                                   &first_block, &dfops,
-                                   &done);
+               error = xfs_bunmapi(tp, ip, first_unmap_block, unmap_len, flags,
+                                   XFS_ITRUNC_MAX_EXTENTS, &first_block,
+                                   &dfops, &done);
                if (error)
                        goto out_bmap_cancel;
 

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 1eebc53..3dd3201 100644 (file)
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -415,8 +415,8 @@ uint                xfs_ilock_attr_map_shared(struct xfs_inode *);
 uint           xfs_ip2xflags(struct xfs_inode *);
 int            xfs_ifree(struct xfs_trans *, xfs_inode_t *,
                           struct xfs_defer_ops *);
-int            xfs_itruncate_extents(struct xfs_trans **, struct xfs_inode *,
-                                     int, xfs_fsize_t);
+int            __xfs_itruncate_extents(struct xfs_trans **, struct xfs_inode *,
+                                       int, xfs_fsize_t, bool);
 void           xfs_iext_realloc(xfs_inode_t *, int, int);
 
 void           xfs_iunpin_wait(xfs_inode_t *);
@@ -433,6 +433,26 @@ int                xfs_dir_ialloc(struct xfs_trans **, struct xfs_inode *, umode_t,
                               xfs_nlink_t, dev_t, prid_t,
                               struct xfs_inode **);
 
+static inline int
+xfs_itruncate_extents(
+       struct xfs_trans        **tpp,
+       struct xfs_inode        *ip,
+       int                     whichfork,
+       xfs_fsize_t             new_size)
+{
+       return __xfs_itruncate_extents(tpp, ip, whichfork, new_size, false);
+}
+
+static inline int
+xfs_itruncate_extents_nodiscard(
+       struct xfs_trans        **tpp,
+       struct xfs_inode        *ip,
+       int                     whichfork,
+       xfs_fsize_t             new_size)
+{
+       return __xfs_itruncate_extents(tpp, ip, whichfork, new_size, true);
+}
+
 /* from xfs_file.c */
 enum xfs_prealloc_flags {
        XFS_PREALLOC_SET        = (1 << 1),