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Date: Fri, 14 Feb 2025 07:22:52 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Carlos Maiolino <cem@kernel.org>,
	Hans Holmberg <hans.holmberg@wdc.com>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 25/43] xfs: implement buffered writes to zoned RT
 devices
Message-ID: <20250214062252.GB25903@lst.de>
References: <20250206064511.2323878-1-hch@lst.de> <20250206064511.2323878-26-hch@lst.de> <20250212005405.GH21808@frogsfrogsfrogs> <20250213053943.GA18867@lst.de> <20250213230558.GX21808@frogsfrogsfrogs>
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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.