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

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Message-ID: <ZyG3GAvTHpRL9tnU@infradead.org>
Date: Tue, 29 Oct 2024 21:33:28 -0700
From: Christoph Hellwig <hch@...radead.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	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 Tue, Oct 29, 2024 at 09:30:41PM -0700, John Hubbard wrote:
> I do, yes. And what happens is that when you use GPUs, drivers like
> to pin system memory, and then point the GPU page tables to that
> memory. For older GPUs that don't support replayable page faults,
> that's required.
> 
> So this behavior has been around forever.
> 
> The customer was qualifying their software and noticed that before
> Linux 6.10, they could allocate >2GB, and with 6.11, they could
> not.
> 
> Whether it is "wise" for user space to allocate that much at once
> is a reasonable question, but at least one place is (or was!) doing
> it.

Still missing a callchain, which make me suspect that it is your weird
out of tree driver, in which case this simply does not matter.