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[49.180.20.59]) by smtp.gmail.com with ESMTPSA id v22-20020aa78516000000b0068fde95aa93sm244484pfn.135.2023.10.02.20.32.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Oct 2023 20:32:18 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1qnW8u-008jvm-0S; Tue, 03 Oct 2023 14:32:16 +1100 Date: Tue, 3 Oct 2023 14:32:16 +1100 From: Dave Chinner To: John Garry Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, chandan.babu@oracle.com, dchinner@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com, linux-api@vger.kernel.org Subject: Re: [PATCH 15/21] fs: xfs: Support atomic write for statx Message-ID: References: <20230929102726.2985188-1-john.g.garry@oracle.com> <20230929102726.2985188-16-john.g.garry@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230929102726.2985188-16-john.g.garry@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Fri, Sep 29, 2023 at 10:27:20AM +0000, John Garry wrote: > Support providing info on atomic write unit min and max for an inode. > > For simplicity, currently we limit the min at the FS block size, but a > lower limit could be supported in future. > > The atomic write unit min and max is limited by the guaranteed extent > alignment for the inode. > > Signed-off-by: John Garry > --- > fs/xfs/xfs_iops.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++ > fs/xfs/xfs_iops.h | 4 ++++ > 2 files changed, 55 insertions(+) > > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c > index 1c1e6171209d..5bff80748223 100644 > --- a/fs/xfs/xfs_iops.c > +++ b/fs/xfs/xfs_iops.c > @@ -546,6 +546,46 @@ xfs_stat_blksize( > return PAGE_SIZE; > } > > +void xfs_ip_atomic_write_attr(struct xfs_inode *ip, > + xfs_filblks_t *unit_min_fsb, > + xfs_filblks_t *unit_max_fsb) Formatting. Also, we don't use variable name shorthand for function names - xfs_get_atomic_write_hint(ip) to match xfs_get_extsz_hint(ip) would be appropriate, right? > +{ > + xfs_extlen_t extsz_hint = xfs_get_extsz_hint(ip); > + struct xfs_buftarg *target = xfs_inode_buftarg(ip); > + struct block_device *bdev = target->bt_bdev; > + struct xfs_mount *mp = ip->i_mount; > + xfs_filblks_t atomic_write_unit_min, > + atomic_write_unit_max, > + align; > + > + atomic_write_unit_min = XFS_B_TO_FSB(mp, > + queue_atomic_write_unit_min_bytes(bdev->bd_queue)); > + atomic_write_unit_max = XFS_B_TO_FSB(mp, > + queue_atomic_write_unit_max_bytes(bdev->bd_queue)); These should be set in the buftarg at mount time, like we do with sector size masks. Then we don't need to convert them to fsbs on every single lookup. > + /* for RT, unset extsize gives hint of 1 */ > + /* for !RT, unset extsize gives hint of 0 */ > + if (extsz_hint && (XFS_IS_REALTIME_INODE(ip) || > + (ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN))) Logic is non-obvious. The compound is (rt || force), not (extsz && rt), so it took me a while to actually realise I read this incorrectly. if (extsz_hint && (XFS_IS_REALTIME_INODE(ip) || (ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN))) { > + align = extsz_hint; > + else > + align = 1; And now the logic looks wrong to me. We don't want to use extsz hint for RT inodes if force align is not set, this will always use it regardless of the fact it has nothing to do with force alignment. Indeed, if XFS_DIFLAG2_FORCEALIGN is not set, then shouldn't this always return min/max = 0 because atomic alignments are not in us on this inode? i.e. the first thing this code should do is: *unit_min_fsb = 0; *unit_max_fsb = 0; if (!(ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN)) return; Then we can check device support: if (!buftarg->bt_atomic_write_max) return; Then we can check for extent size hints. If that's not set: align = xfs_get_extsz_hint(ip); if (align <= 1) { unit_min_fsb = 1; unit_max_fsb = 1; return; } And finally, if there is an extent size hint, we can return that. > + if (atomic_write_unit_max == 0) { > + *unit_min_fsb = 0; > + *unit_max_fsb = 0; > + } else if (atomic_write_unit_min == 0) { > + *unit_min_fsb = 1; > + *unit_max_fsb = min_t(xfs_filblks_t, atomic_write_unit_max, > + align); Why is it valid for a device to have a zero minimum size? If it can set a maximum, it should -always- set a minimum size as logical sector size is a valid lower bound, yes? > + } else { > + *unit_min_fsb = min_t(xfs_filblks_t, atomic_write_unit_min, > + align); > + *unit_max_fsb = min_t(xfs_filblks_t, atomic_write_unit_max, > + align); > + } Nothing here guarantees the power-of-2 sizes that the RWF_ATOMIC user interface requires.... It also doesn't check that the extent size hint is aligned with atomic write units. It also doesn't check either against stripe unit alignment.... > +} > + > STATIC int > xfs_vn_getattr( > struct mnt_idmap *idmap, > @@ -614,6 +654,17 @@ xfs_vn_getattr( > stat->dio_mem_align = bdev_dma_alignment(bdev) + 1; > stat->dio_offset_align = bdev_logical_block_size(bdev); > } > + if (request_mask & STATX_WRITE_ATOMIC) { > + xfs_filblks_t unit_min_fsb, unit_max_fsb; > + > + xfs_ip_atomic_write_attr(ip, &unit_min_fsb, > + &unit_max_fsb); > + stat->atomic_write_unit_min = XFS_FSB_TO_B(mp, unit_min_fsb); > + stat->atomic_write_unit_max = XFS_FSB_TO_B(mp, unit_max_fsb); That's just nasty. We pull byte units from the bdev, convert them to fsb to round them, then convert them back to byte counts. We should be doing all the work in one set of units.... > + stat->attributes |= STATX_ATTR_WRITE_ATOMIC; > + stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC; > + stat->result_mask |= STATX_WRITE_ATOMIC; If the min/max are zero, then atomic writes are not supported on this inode, right? Why would we set any of the attributes or result mask to say it is supported on this file? -Dave. -- Dave Chinner david@fromorbit.com