"lilei.777@xxxxxxxxxxxxx" <lilei.777@xxxxxxxxxxxxx> writes: > Hi Harjani, > > I tend to enable ext4 16kb atomic write on my X86 machine, and read your > RFC. > https://lwn.net/ml/linux-kernel/cover.1709356594.git.ritesh.list@xxxxxxxxx/ Hi Lei, This is the final version which got merged [1] [1]: https://lore.kernel.org/all/cover.1730437365.git.ritesh.list@xxxxxxxxx/ On x86, we don't have bs > ps feature. And as of today iomap restricts the atomic write to a single filesystem block. Hence for systems with 4k pagesize, we can't have atomic write request of size 16k on a 4k blocksize ext4. But on arm64 or powerpc (with 64k ps) we should be able to enable this with 16k bs, because ext4 can work with bs < ps. > > From the cover patch, it's seems that this feature will be successfully > enabled > if I enable bigalloc on ext4, and underlying device also supports 16kb > write union. Yes, there are still ongoing discussions around this in the community [1][2]. [1]: https://lore.kernel.org/all/Z5nTaQgLGdD6hSvL@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ [2]: https://lore.kernel.org/linux-xfs/20241204154344.3034362-1-john.g.garry@xxxxxxxxxx/ -ritesh > However, after checking xstat result, i found atomic_write_unit_max was > always 4096. > > This snippet below limits s_awu_max to 4096(bs) which is the max value on > my platform. > > ``` > static void ext4_atomic_write_init(struct super_block *sb) > { > ... > sbi->s_awu_min = max(sb->s_blocksize, > bdev_atomic_write_unit_min_bytes(bdev)); > sbi->s_awu_max = min(sb->s_blocksize, > bdev_atomic_write_unit_max_bytes(bdev)); > ... > } > ``` > > I am wondering if I missed someting? Or if there any other ways could > enable 16kb > atomic write on my platform? > > Thanks! > Li Lei
