linux-kernel - Re: [PATCH 4/6] fs: xfs: Support atomic write for statx

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Message-ID: <ZcoJossEQe6QIIM+@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date: Mon, 12 Feb 2024 17:35:54 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: John Garry <john.g.garry@...cle.com>
Cc: hch@....de, djwong@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org,
        dchinner@...hat.com, jack@...e.cz, chandan.babu@...cle.com,
        martin.petersen@...cle.com, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        tytso@....edu, jbongio@...gle.com
Subject: Re: [PATCH 4/6] fs: xfs: Support atomic write for statx

On Fri, Feb 09, 2024 at 05:30:50PM +0000, John Garry wrote:
> The same goes for atomic write boundary in NVMe. Currently we say that it
> needs to be a power-of-2. However, it really just needs to be a multiple of
> awu_max. So if some HW did report a !power-of-2 atomic write boundary, we

Hey John, sorry for double reply but can you point out where this
requrement is stated in the spec?

For example in NVME 2.1.4.3 Command Set spec I can see that

> The boundary size shall be greater than or equal to the corresponding
> atomic write size

However I'm not able to find the multiple-of-unit-max reqirement in the
spec. Maybe I'm missing something?

Regards,
ojaswin

> could reduce awu_max reported until to fits the power-of-2 rule and also is
> cleanly divisible into atomic write boundary. But that is just not what HW
> will report (I expect). We live in a power-of-2 data granularity world.