linux-kernel - Re: [PATCH v5 00/10] block atomic writes

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Message-ID: <ZeembVG-ygFal6Eb@casper.infradead.org>
Date: Tue, 5 Mar 2024 23:10:37 +0000
From: Matthew Wilcox <willy@...radead.org>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
	jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
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	ritesh.list@...il.com
Subject: Re: [PATCH v5 00/10] block atomic writes

On Mon, Feb 26, 2024 at 05:36:02PM +0000, John Garry wrote:
> This series introduces a proposal to implementing atomic writes in the
> kernel for torn-write protection.

The API as documented will be unnecessarily complicated to implement
for buffered writes, I believe.  What I would prefer is a chattr (or, I
guess, setxattr these days) that sets the tearing boundary for the file.
The page cache can absorb writes of arbitrary size and alignment, but
will be able to guarantee that (if the storage supports it), the only
write tearing will happen on the specified boundary.

We _can_ support arbitrary power-of-two write sizes to the page cache,
but if the requirement is no tearing inside a single write, then we
will have to do a lot of work to make that true.  It isn't clear to me
that anybody is asking for this; the databases I'm aware of are willing
to submit 128kB writes and accept that there may be tearing at 16kB
boundaries (or whatever).