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>
> ---
> 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;
Please just replace the whichfork argument to xfs_itruncate_extents
with a bmapi_flags one, and e'll get a much simpler interface.
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