linux-kernel - Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma

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Message-ID: <Zec_nAQn1Ft_ZTHH@kbusch-mbp.dhcp.thefacebook.com>
Date: Tue, 5 Mar 2024 08:51:56 -0700
From: Keith Busch <kbusch@...nel.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Chaitanya Kulkarni <chaitanyak@...dia.com>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Jonathan Corbet <corbet@....net>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>, Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	kvm@...r.kernel.org, linux-mm@...ck.org,
	Bart Van Assche <bvanassche@....org>,
	Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
	Amir Goldstein <amir73il@...il.com>,
	"josef@...icpanda.com" <josef@...icpanda.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"daniel@...earbox.net" <daniel@...earbox.net>,
	Dan Williams <dan.j.williams@...el.com>,
	"jack@...e.com" <jack@...e.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Zhu Yanjun <zyjzyj2000@...il.com>
Subject: Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma_map() for NVMe SGL

On Tue, Mar 05, 2024 at 01:18:47PM +0200, Leon Romanovsky wrote:
> @@ -236,7 +236,9 @@ struct nvme_iod {
>  	unsigned int dma_len;	/* length of single DMA segment mapping */
>  	dma_addr_t first_dma;
>  	dma_addr_t meta_dma;
> -	struct sg_table sgt;
> +	struct dma_iova_attrs iova;
> +	dma_addr_t dma_link_address[128];
> +	u16 nr_dma_link_address;
>  	union nvme_descriptor list[NVME_MAX_NR_ALLOCATIONS];
>  };

That's quite a lot of space to add to the iod. We preallocate one for
every request, and there could be millions of them.