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Message-ID: <20231128135619.GA12202@lst.de>
Date: Tue, 28 Nov 2023 14:56:19 +0100
From: Christoph Hellwig <hch@....de>
To: John Garry <john.g.garry@...cle.com>
Cc: Christoph Hellwig <hch@....de>, axboe@...nel.dk, kbusch@...nel.org,
sagi@...mberg.me, jejb@...ux.ibm.com, martin.petersen@...cle.com,
djwong@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org,
chandan.babu@...cle.com, dchinner@...hat.com,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
linux-api@...r.kernel.org
Subject: Re: [PATCH 17/21] fs: xfs: iomap atomic write support
On Tue, Nov 28, 2023 at 08:56:37AM +0000, John Garry wrote:
> Are you suggesting some sort of hybrid between the atomic write series you
> had a few years ago and this solution?
Very roughly, yes.
> To me that would be continuing with the following:
> - per-IO RWF_ATOMIC (and not O_ATOMIC semantics of nothing is written until
> some data sync)
Yes.
> - writes must be a power-of-two and at a naturally-aligned offset
Where offset is offset in the file? It would not require it. You
probably want to do it for optimal performance, but requiring it
feeels rather limited.
> - relying on atomic write HW support always
And I think that's where we have different opinions. I think the hw
offload is a nice optimization and we should use it wherever we can.
But building the entire userspace API around it feels like a mistake.
> BTW, we also have rtvol support which does not use forcealign as it already
> can guarantee alignment, but still does rely on the same principle of
> requiring alignment - would you want CoW support there also?
Upstream doesn't have out of place write support for the RT subvolume
yet. But Darrick has a series for it and we're actively working on
upstreaming it.
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