linux-kernel - Re: [PATCH v20 07/12] nvme: add copy offload support

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Message-ID: <20240601062219.GB6221@lst.de>
Date: Sat, 1 Jun 2024 08:22:19 +0200
From: Christoph Hellwig <hch@....de>
To: Nitesh Shetty <nj.shetty@...sung.com>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
	Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	martin.petersen@...cle.com, bvanassche@....org, david@...morbit.com,
	hare@...e.de, damien.lemoal@...nsource.wdc.com,
	anuj20.g@...sung.com, joshi.k@...sung.com, nitheshshetty@...il.com,
	gost.dev@...sung.com, Javier Gonz??lez <javier.gonz@...sung.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, dm-devel@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 07/12] nvme: add copy offload support

On Mon, May 20, 2024 at 03:50:20PM +0530, Nitesh Shetty wrote:
> +	if (blk_rq_nr_phys_segments(req) != BLK_COPY_MAX_SEGMENTS)
> +		return BLK_STS_IOERR;

This sounds like BLK_COPY_MAX_SEGMENTS is misnamed.  Right now this is
not a max segments, but the exact number of segments required.

>  /*
>   * Recommended frequency for KATO commands per NVMe 1.4 section 7.12.1:
> - * 
> + *

Please submit this whitespace fix separately.

> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 8b1edb46880a..1c5974bb23d5 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1287,6 +1287,7 @@ static inline unsigned int bdev_discard_granularity(struct block_device *bdev)
>  
>  /* maximum copy offload length, this is set to 128MB based on current testing */
>  #define BLK_COPY_MAX_BYTES		(1 << 27)
> +#define BLK_COPY_MAX_SEGMENTS		2

... and this doesn't belong into a NVMe patch.  I'd also expect that
the block layer would verify this before sending of the request to the driver.

> diff --git a/include/linux/nvme.h b/include/linux/nvme.h
> index 425573202295..5275a0962a02 100644
> --- a/include/linux/nvme.h
> +++ b/include/linux/nvme.h

Note that we've usually kept adding new protocol bits to nvme.h separate
from the implementation in the host or target code.