linux-kernel - Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a time

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Message-ID: <fa766610-4a0c-4d75-90fd-6c781fadee73@nvidia.com>
Date: Tue, 29 Oct 2024 21:44:52 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
 linux-stable@...r.kernel.org, Vivek Kasireddy <vivek.kasireddy@...el.com>,
 David Hildenbrand <david@...hat.com>, Dave Airlie <airlied@...hat.com>,
 Gerd Hoffmann <kraxel@...hat.com>, Matthew Wilcox <willy@...radead.org>,
 Jason Gunthorpe <jgg@...dia.com>, Peter Xu <peterx@...hat.com>,
 Arnd Bergmann <arnd@...db.de>, Daniel Vetter <daniel.vetter@...ll.ch>,
 Dongwon Kim <dongwon.kim@...el.com>, Hugh Dickins <hughd@...gle.com>,
 Junxiao Chang <junxiao.chang@...el.com>,
 Mike Kravetz <mike.kravetz@...cle.com>, Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a
 time

On 10/29/24 9:42 PM, Christoph Hellwig wrote:
> On Tue, Oct 29, 2024 at 09:39:15PM -0700, John Hubbard wrote:
>> I expect I could piece together something with Nouveau, given enough
>> time and help from Ben Skeggs and Danillo and all...
>>
>> Yes, this originated with the out of tree driver. But it never occurred
>> to me that upstream be uninterested in an obvious fix to an obvious
>> regression.
> 
> Because pinning down these amounts of memoryt is completely insane.
> I don't mind the switch to kvmalloc, but we need to put in an upper
> bound of what can be pinned.

I'm wondering though, how it is that we decide how much of the user's
system we prevent them from using? :)  People with hardware accelerators
do not always have page fault capability, and yet these troublesome
users insist on stacking their system full of DRAM and then pointing
the accelerator to it.

How would we choose a value? Memory sizes keep going up...


thanks,
-- 
John Hubbard