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

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Date: Tue, 28 May 2024 10:21:15 +0100
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@...radead.org>
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 23/05/2024 13:59, Christoph Hellwig wrote:
> 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.

Is this what you are talking about:

https://web.eecs.umich.edu/~tpkelly/papers/Failure_atomic_msync_EuroSys_2013.pdf

If so, I am not sure if a mmap interface would work for DB usecase, like 
PostgreSQL. I can ask.