linux-kernel - Re: [PATCH v4 00/14] forcealign for xfs

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Message-ID: <20240924061719.GA11211@lst.de>
Date: Tue, 24 Sep 2024 08:17:19 +0200
From: Christoph Hellwig <hch@....de>
To: John Garry <john.g.garry@...cle.com>
Cc: Christoph Hellwig <hch@....de>, Dave Chinner <david@...morbit.com>,
	Ritesh Harjani <ritesh.list@...il.com>, chandan.babu@...cle.com,
	djwong@...nel.org, dchinner@...hat.com, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	catherine.hoang@...cle.com, martin.petersen@...cle.com
Subject: Re: [PATCH v4 00/14] forcealign for xfs

On Mon, Sep 23, 2024 at 01:33:12PM +0100, John Garry wrote:
>> As a first step by not making it worse, and that not only means not
>> spreading the rtextent stuff further,
>
> I assume that refactoring rtextent into "big alloc unit" is spreading 
> (rtextent stuff), right? If so, what other solution? CoW?

Well, if you look at the force align series you'd agree that it
spreads the thing out into the btree allocator.  Or do I misread it?

>
>> but more importantly not introducing
>> additional complexities by requiring to be able to write over the
>> written/unwritten boundaries created by either rtextentsize > 1 or
>> the forcealign stuff if you actually want atomic writes.
>
> The very original solution required a single mapping and in written state 
> for atomic writes. Reverting to that would save a lot of hassle in the 
> kernel. It just means that the user needs to manually pre-zero.

What atomic I/O sizes do your users require?  Would they fit into
a large sector size now supported by XFS (i.e. 32k for now).