netdev - Re: [PATCH net-next 2/3] mm: vmalloc: export find_vm

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Message-ID: <20260128180629.GT1641016@ziepe.ca>
Date: Wed, 28 Jan 2026 14:06:29 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: Leon Romanovsky <leon@...nel.org>, Uladzislau Rezki <urezki@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dust Li <dust.li@...ux.alibaba.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Sidraya Jayagond <sidraya@...ux.ibm.com>,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Mahanta Jambigi <mjambigi@...ux.ibm.com>,
	Simon Horman <horms@...nel.org>, Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-rdma@...r.kernel.org,
	linux-s390@...r.kernel.org, netdev@...r.kernel.org,
	oliver.yang@...ux.alibaba.com
Subject: Re: [PATCH net-next 2/3] mm: vmalloc: export find_vm_area()

On Wed, Jan 28, 2026 at 11:45:58AM +0800, D. Wythe wrote:

> By leveraging vmalloc_huge() and the proposed helper to increase the
> page_size in ib_map_mr_sg(), each MTTE covers a much larger contiguous
> physical block.

This doesn't seem right, if your goal is to take a vmalloc() pointer
and convert it to a MR via a scatterlist and ib_map_mr_sg() then you
should be asking for a helper to convert a kernel pointer into a
scatterlist.

Even if you do this in a naive way and call the
sg_alloc_append_table_from_pages() function it will automatically join
physically contiguous ranges together for you.

>From there you can check the resulting scatterlist and compute the
page_size to pass to ib_map_mr_sg().

No need to ask the MM for anything other than the list of physicals to
build the scatterlist with.

Still, I wouldn't mind seeing a helper to convert a kernel pointer
into a scatterlist because I have see that opencoded in a few places,
and maybe there are ways to optimize that using more information from
the MM - but it should be APIs used only by this helper not exposed to
drivers.

Jason