On Mon, Sep 16, 2024 at 10:44:38AM +0100, John Garry wrote: > > > > * I guess that you had not been following the recent discussion on this > > > topic in the latest xfs atomic writes series @ https://urldefense.com/v3/__https://lore.kernel.org/linux-xfs/20240817094800.776408-1-john.g.garry@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!JIzCbkyp3JuPyzBx1n80WAdog5rLxMRB65FYrs1sFf3ei-wOdqrU_DZBE5zwrJXhrj949HSE0TwOEV0ciu8$ > > > and also mentioned earlier in > > > https://urldefense.com/v3/__https://lore.kernel.org/linux-xfs/20240726171358.GA27612@xxxxxx/__;!!ACWV5N9M2RV99hQ!JIzCbkyp3JuPyzBx1n80WAdog5rLxMRB65FYrs1sFf3ei-wOdqrU_DZBE5zwrJXhrj949HSE0TwOiiEnYSk$ > > > > > > There I dropped the sub-alloc unit zeroing. The concept to iter for a single > > > bio seems sane, but as Darrick mentioned, we have issue of non-atomically > > > committing all the extent conversions. > > > > Yes, I understand these problems exist. My entire point is that the > > forced alignment implemention should never allow such unaligned > > extent patterns to be created in the first place. If we avoid > > creating such situations in the first place, then we never have to > > care about about unaligned unwritten extent conversion breaking > > atomic IO. > > OK, but what about this situation with non-EOF unaligned extents: > > # xfs_io -c "lsattr -v" mnt/file > [extsize, has-xattr, force-align] mnt/file > # xfs_io -c "extsize" mnt/file > [65536] mnt/file > # > # xfs_io -d -c "pwrite 64k 64k" mnt/file > # xfs_io -d -c "pwrite 8k 8k" mnt/file > # xfs_bmap -vvp mnt/file > mnt/file: > EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS > 0: [0..15]: 384..399 0 (384..399) 16 010000 > 1: [16..31]: 400..415 0 (400..415) 16 000000 > 2: [32..127]: 416..511 0 (416..511) 96 010000 > 3: [128..255]: 256..383 0 (256..383) 128 000000 > FLAG Values: > 0010000 Unwritten preallocated extent > > Here we have unaligned extents wrt extsize. > > The sub-alloc unit zeroing would solve that - is that what you would still > advocate (to solve that issue)? Yes, I thought that was already implemented for force-align with the DIO code via the extsize zero-around changes in the iomap code. Why isn't that zero-around code ensuring the correct extent layout here? > > FWIW, I also understand things are different if we are doing 128kB > > atomic writes on 16kB force aligned files. However, in this > > situation we are treating the 128kB atomic IO as eight individual > > 16kB atomic IOs that are physically contiguous. > > Yes, if 16kB force aligned, userspace can only issue 16KB atomic writes. Right, but the eventual goal (given the statx parameters) is to be able to do 8x16kB sequential atomic writes as a single 128kB IO, yes? > > > > Again, this is different to the traditional RT file behaviour - it > > > > can use unwritten extents for sub-alloc-unit alignment unmaps > > > > because the RT device can align file offset to any physical offset, > > > > and issue unaligned sector sized IO without any restrictions. Forced > > > > alignment does not have this freedom, and when we extend forced > > > > alignment to RT files, it will not have the freedom to use > > > > unwritten extents for sub-alloc-unit unmapping, either. > > > > > > > So how do you think that we should actually implement > > > xfs_itruncate_extents_flags() properly for forcealign? Would it simply be > > > like: > > > > > > --- a/fs/xfs/xfs_inode.c > > > +++ b/fs/xfs/xfs_inode.c > > > @@ -1050,7 +1050,7 @@ xfs_itruncate_extents_flags( > > > WARN_ON_ONCE(first_unmap_block > XFS_MAX_FILEOFF); > > > return 0; > > > } > > > + if (xfs_inode_has_forcealign(ip)) > > > + first_unmap_block = xfs_inode_roundup_alloc_unit(ip, > > > first_unmap_block); > > > error = xfs_bunmapi_range(&tp, ip, flags, first_unmap_block, > > > > Yes, it would be something like that, except it would have to be > > done before first_unmap_block is verified. > > > > ok, and are you still of the opinion that this does not apply to rtvol? The rtvol is *not* force-aligned. It -may- have some aligned allocation requirements that are similar (i.e. sb_rextsize > 1 fsb) but it does *not* force-align extents, written or unwritten. The moment we add force-align support to RT files (as is the plan), then the force-aligned inodes on the rtvol will need to behave as force aligned inodes, not "rtvol" inodes. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
