On Tue, May 08, 2018 at 01:22:30PM -0400, Brian Foster wrote:
> 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@xxxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_bmap_util.c | 4 ++--
> fs/xfs/xfs_inode.c | 19 +++++++++++--------
> fs/xfs/xfs_inode.h | 24 ++++++++++++++++++++++--
> 3 files changed, 35 insertions(+), 12 deletions(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 8cd8c412f52d..696c3b6bd2c9 100644
> --- 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 2b70c8b4cee2..d63ddd806074 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1534,11 +1534,12 @@ 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;
> @@ -1549,6 +1550,7 @@ 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) ||
> @@ -1561,6 +1563,10 @@ 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
> @@ -1579,12 +1585,9 @@ 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 1eebc53df7d7..3dd3201f4409 100644
> --- 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),
> --
> 2.14.3
>
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