linux-kernel - Re: [PATCH v2 1/2] nvme-pci: Use size_t for length fields to handle larger sizes

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Message-ID: <20251118050311.GA21569@lst.de>
Date: Tue, 18 Nov 2025 06:03:11 +0100
From: Christoph Hellwig <hch@....de>
To: Leon Romanovsky <leon@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
	Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org, Chaitanya Kulkarni <kch@...dia.com>
Subject: Re: [PATCH v2 1/2] nvme-pci: Use size_t for length fields to
 handle larger sizes

On Mon, Nov 17, 2025 at 09:22:43PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> This patch changes the length variables from unsigned int to size_t.
> Using size_t ensures that we can handle larger sizes, as size_t is
> always equal to or larger than the previously used u32 type.
> 
> Originally, u32 was used because blk-mq-dma code evolved from
> scatter-gather implementation, which uses unsigned int to describe length.
> This change will also allow us to reuse the existing struct phys_vec in places
> that don't need scatter-gather.
> 
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
> ---
>  block/blk-mq-dma.c      | 8 ++++++--
>  drivers/nvme/host/pci.c | 4 ++--
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
> index e9108ccaf4b0..e7d9b54c3eed 100644
> --- a/block/blk-mq-dma.c
> +++ b/block/blk-mq-dma.c
> @@ -8,7 +8,7 @@
>  
>  struct phys_vec {
>  	phys_addr_t	paddr;
> -	u32		len;
> +	size_t		len;
>  };

So we're now going to increase memory usage by 50% again after just
reducing it by removing the scatterlist?