linux-kernel - Re: [PATCH v7 11/14] xfs: add xfs_file_dio_write

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Message-ID: <94141f35-5293-44dc-8b98-12a0d27fdcd7@oracle.com>
Date: Wed, 23 Apr 2025 08:02:00 +0100
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>, brauner@...nel.org,
        djwong@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz,
        cem@...nel.org, linux-fsdevel@...r.kernel.org, dchinner@...hat.com,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        ojaswin@...ux.ibm.com, ritesh.list@...il.com,
        martin.petersen@...cle.com, linux-ext4@...r.kernel.org,
        linux-block@...r.kernel.org, catherine.hoang@...cle.com,
        linux-api@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>,
        Daniel Gomez <da.gomez@...sung.com>
Subject: Re: [PATCH v7 11/14] xfs: add xfs_file_dio_write_atomic()

On 23/04/2025 06:44, Christoph Hellwig wrote:
> On Tue, Apr 22, 2025 at 07:08:32AM +0100, John Garry wrote:
>> So consider userspace wants to write something atomically and we fail as a
>> HW-based atomic write is not possible. What is userspace going to do next?
> Exactly.
> 
>> I heard something like "if HW-based atomics are not possible, then
>> something has not been configured properly for the FS" - that something
>> would be extent granularity and alignment, but we don't have a method to
>> ensure this. That is the whole point of having a FS fallback.
> We now have the opt limit, right? 

right

> (I'll review the reposted series
> ASAP, 

ok, cheers

> but for now I'll assume it)  They can just tune their applications
> to it, and trigger on a trace point for the fallback to monitor it.