Re: [PATCH 25/43] xfs: implement buffered writes to zoned RT devices

Darrick J. Wong
2025-02-14T18:29:54Z

On Fri, Feb 14, 2025 at 07:22:52AM +0100, Christoph Hellwig wrote:
> On Thu, Feb 13, 2025 at 03:05:58PM -0800, Darrick J. Wong wrote:
> > > we'll need a space allocation for every write in an out of tree write
> > > file system. But -ENOSPC (or SIGBUS for the lovers of shared mmap
> > > based I/O :)) on writes is very much expected. On truncate a lot less
> > > so. In fact not dipping into the reserved pool here for example breaks
> > > rocksdb workloads.
> >
> > It occurs to me that regular truncate-down on a shared block can also
> > return ENOSPC if the filesystem is completely out of space. Though I
> > guess in that case, at least df will say that nearly zero space is
> > available, whereas for zoned storage we might have plenty of free space
> > that simply isn't available right now... right?
>
> That's part of it, yes as we can't kick GC. That reason will go away
> if/when the VFS locking for truncates is fixed. But I also doubt people
> run nasty workloads on reflinked files all that much.

<nod> The nasty reflink workloads are mostly disk images, and those
aren't getting small truncations.

--D