linux-kernel - Re: [LSF/MM/BPF TOPIC] untorn buffered writes

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Date: Thu, 23 May 2024 05:59:40 -0700
From: Christoph Hellwig <hch@...radead.org>
To: John Garry <john.g.garry@...cle.com>
Cc: Theodore Ts'o <tytso@....edu>, lsf-pc@...ts.linux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Matthew Wilcox <willy@...radead.org>,
	Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org
Subject: Re: [LSF/MM/BPF TOPIC] untorn buffered writes

On Wed, May 15, 2024 at 01:54:39PM -0600, John Garry wrote:
> On 27/02/2024 23:12, Theodore Ts'o wrote:
> > Last year, I talked about an interest to provide database such as
> > MySQL with the ability to issue writes that would not be torn as they
> > write 16k database pages[1].
> > 
> > [1] https://urldefense.com/v3/__https://lwn.net/Articles/932900/__;!!ACWV5N9M2RV99hQ!Ij_ZeSZrJ4uPL94Im73udLMjqpkcZwHmuNnznogL68ehu6TDTXqbMsC4xLUqh18hq2Ib77p1D8_4mV5Q$
> > 
> 
> After discussing this topic earlier this week, I would like to know if there
> are still objections or concerns with the untorn-writes userspace API
> proposed in https://lore.kernel.org/linux-block/20240326133813.3224593-1-john.g.garry@oracle.com/
> 
> I feel that the series for supporting direct-IO only, above, is stuck
> because of this topic of buffered IO.

Just my 2 cents, but I think supporting untorn I/O for buffered I/O
is an amazingly bad idea that opens up a whole can of worms in terms
of potential failure paths while not actually having a convincing use
case.

For buffered I/O something like the atomic msync proposal makes a lot
more sense, because it actually provides a useful API for non-trivial
transactions.