linux-kernel - Re: [PATCH 01/21] block: Add atomic write operations to request

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Message-ID: <45bc1c01-09c7-4c54-b305-f349d0d0e19b@acm.org>
Date:   Wed, 4 Oct 2023 14:00:58 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     John Garry <john.g.garry@...cle.com>, axboe@...nel.dk,
        kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.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,
        Himanshu Madhani <himanshu.madhani@...cle.com>
Subject: Re: [PATCH 01/21] block: Add atomic write operations to request_queue
 limits

On 10/3/23 20:00, Martin K. Petersen wrote:
> 
> Bart,
> 
>>    also that there are no guarantees that the data written by an atomic
>>    write will survive a power failure. See also the difference between
>>    the NVMe parameters AWUN and AWUPF.
> 
> We only care about *PF. The *N variants were cut from the same cloth as
> TRIM and UNMAP.

Hi Martin,

Has the following approach been considered? RWF_ATOMIC only guarantees 
atomicity. Persistence is not guaranteed without fsync() / fdatasync().

I think this would be more friendly towards battery-powered devices
(smartphones). On these devices it can be safe to skip fsync() / 
fdatasync() if the battery level is high enough.

Thanks,

Bart.