On Mon, Sep 16, 2024 at 11:24:56AM +0100, John Garry wrote: > On 16/09/2024 08:03, Dave Chinner wrote: > > OTOH, we can't do this with atomic writes. Atomic writes require > > some mkfs help because they require explicit physical alignment of > > the filesystem to the underlying storage. Forcealign requires agsize%extsize==0, it's atomicwrites that adds the requirement that extsize be a power of 2... > If we are enabling atomic writes at mkfs time, then we can ensure agsize % > extsize == 0. That provides the physical alignment guarantee. It also makes > sense to ensure extsize is a power-of-2. > > However, extsize is re-configurble per inode. So, for an inode enabled for > atomic writes, we must still ensure agsize % new extsize == 0 (and also new > extsize is a power-of-2) ...so yes. > > Hence we'll eventually end > > up with atomic writes needing to be enabled at mkfs time, but force > > align will be an upgradeable feature flag. > > Could atomic writes also be an upgradeable feature? We just need to ensure > that agsize % extsize == 0 for an inode enabled for atomic writes. Valid > extsize values may be quite limited, though, depending on the value of > agsize. I don't see why forcealign and atomicwrites can't be added to the sb featureset after the fact, though you're right that callers of xfs_io chattr might be hard pressed to find an fsx_extsize value that fits. --D > Thanks, > John > >
