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Message-ID: <b5af0cd4-033b-42d6-a147-ec8bc8956b2f@oracle.com>
Date: Wed, 14 Feb 2024 09:21:18 +0000
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v3 14/15] nvme: Support atomic writes
To: Christoph Hellwig <hch@lst.de>
Cc: axboe@kernel.dk, kbusch@kernel.org, sagi@grimberg.me, jejb@linux.ibm.com,
        martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk,
        brauner@kernel.org, dchinner@redhat.com, jack@suse.cz,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
        linux-scsi@vger.kernel.org, ming.lei@redhat.com, ojaswin@linux.ibm.com,
        bvanassche@acm.org, Alan Adamson <alan.adamson@oracle.com>
References: <20240124113841.31824-1-john.g.garry@oracle.com>
 <20240124113841.31824-15-john.g.garry@oracle.com>
 <20240213064204.GB23305@lst.de>
 <0323ba69-dff9-4465-817e-2c349141b753@oracle.com>
 <20240214080024.GA10357@lst.de>
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From: John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <20240214080024.GA10357@lst.de>
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On 14/02/2024 08:00, Christoph Hellwig wrote:
> On Tue, Feb 13, 2024 at 02:21:25PM +0000, John Garry wrote:
>>> Please also read through TP4098(a) and look at the MAM field.
>>
>> It's not public, AFAIK.
> 
> Oracle is a member, so you can take a look at it easily.  If we need
> it for Linux I can also work with the NVMe Board to release it.

What I really meant was that I prefer not to quote private TPs in public 
domain. I have the doc.

> 
>> And I don't think a feature which allows us to straddle boundaries is too
>> interesting really.
> 
> Without MAM=1 NVMe can't support atomic writes larger than
> AWUPF/NAWUPF, which is typically set to the indirection table
> size.  You're leaving a lot of potential unused with that.
> 

atomic_write_unit_max would always be dictated by min of boundary and 
AWUPF/NAWUPF. With MAM=1, we could increase atomic_write_max_bytes - but 
does it really help us? I mean, atomic_write_max_bytes only comes into 
play for merging - do we get much merging for NVMe transports? I am not 
sure.

Thanks,
John