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Message-ID: <0323ba69-dff9-4465-817e-2c349141b753@oracle.com>
Date: Tue, 13 Feb 2024 14:21:25 +0000
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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>
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From: John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <20240213064204.GB23305@lst.de>
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On 13/02/2024 06:42, Christoph Hellwig wrote:
> On Wed, Jan 24, 2024 at 11:38:40AM +0000, John Garry wrote:
>> From: Alan Adamson <alan.adamson@oracle.com>
>>
>> Support reading atomic write registers to fill in request_queue
>> properties.
>>
>> Use following method to calculate limits:
>> atomic_write_max_bytes = flp2(NAWUPF ?: AWUPF)
>> atomic_write_unit_min = logical_block_size
>> atomic_write_unit_max = flp2(NAWUPF ?: AWUPF)
>> atomic_write_boundary = NABSPF
> 
> Can you expand this to actually be a real commit log with full
> sentences, expanding the NVME field name acronyms and reference
> the relevant Sections and Figures in a specific version of the
> NVMe specification?

ok

> 
> Also some implementation comments:
> 
> NVMe has a particularly nasty NABO field in Identify Namespace, which
> offsets the boundary. We probably need to reject atomic writes or
> severly limit them if this field is set.

ok, and initially we'll just not support atomic writes for NABO != 0

> 
> Please also read through TP4098(a) and look at the MAM field.

It's not public, AFAIK.

And I don't think a feature which allows us to straddle boundaries is 
too interesting really.

>  As far
> as I can tell the patch as-is assumes it always is set to 1.
> 
>> +static void nvme_update_atomic_write_disk_info(struct gendisk *disk,
>> +		struct nvme_ctrl *ctrl, struct nvme_id_ns *id, u32 bs, u32 atomic_bs)
> 
> Please avoid the overly long line here.
> 
>> +		nvme_update_atomic_write_disk_info(disk, ctrl, id, bs, atomic_bs);
> 
> .. and here.

ok, but I think that this will get shorter anyway.

> 

Thanks,
John