On 10/26/20 6:28 AM, Matthew Wilcox wrote:
On Sun, Oct 25, 2020 at 09:44:07PM -0700, John Hubbard wrote:
On 10/25/20 9:21 PM, Matthew Wilcox wrote:
I don't think the page pinning approach is ever valid. For file
Could you qualify that? Surely you don't mean that the entire pin_user_pages
story is a waste of time--I would have expected you to make more noise
earlier if you thought that, yes?
I do think page pinning is the wrong approach for everything. I did say
Not *everything*, just "pinning for DMA", right? Because I don't recall
any viable solutions for Direct IO that avoided gup/pup!
Also, back to Case 5: I *could* create a small patchset to change over
the very few Case 5 call sites to use "gup, lock_page(), write to
page...etc", instead of pup. And also, update pin_user_pages.rst to
recommend that approach in similar situations. After all, it's not
really a long-term DMA pin, which is really what pin_user_pages*() is
intended for.
Would that be something you'd like to see happen? It's certainly easy
enough to fix that up. And your retroactive NAK is sufficient motivation
to do so.
so at the time, and I continue to say so when the opportunity presents
itself. But shouting about it constantly only annoys people, so I don't
generally bother. I have other things to work on, and they're productive,
so I don't need to spend my time arguing.
Sure. As a practical matter, I've assumed that page pinning is not going
to go away any time soon, so I want it to work properly while it's here.
But if there is a viable way to eventually replace dma-pinning with
something better, then let's keep thinking about it. I'm glad to help in
that area.
thanks,
--
John Hubbard
NVIDIA
