Nouveau Archive on lore.kernel.org
 help / color / Atom feed
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Alistair Popple <apopple@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	Nouveau Dev <nouveau@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	kvm-ppc@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
	Ben Skeggs <bskeggs@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau
Date: Tue, 9 Feb 2021 09:35:20 -0400
Message-ID: <20210209133520.GB4718@ziepe.ca> (raw)
In-Reply-To: <3426910.QXTomnrpqD@nvdebian>

On Tue, Feb 09, 2021 at 11:57:28PM +1100, Alistair Popple wrote:
> On Tuesday, 9 February 2021 9:27:05 PM AEDT Daniel Vetter wrote:
> > >
> > > Recent changes to pin_user_pages() prevent the creation of pinned pages in
> > > ZONE_MOVABLE. This series allows pinned pages to be created in 
> ZONE_MOVABLE
> > > as attempts to migrate may fail which would be fatal to userspace.
> > >
> > > In this case migration of the pinned page is unnecessary as the page can 
> be
> > > unpinned at anytime by having the driver revoke atomic permission as it
> > > does for the migrate_to_ram() callback. However a method of calling this
> > > when memory needs to be moved has yet to be resolved so any discussion is
> > > welcome.
> > 
> > Why do we need to pin for gpu atomics? You still have the callback for
> > cpu faults, so you
> > can move the page as needed, and hence a long-term pin sounds like the
> > wrong approach.
> 
> Technically a real long term unmoveable pin isn't required, because as you say 
> the page can be moved as needed at any time. However I needed some way of 
> stopping the CPU page from being freed once the userspace mappings for it had 
> been removed. 

The issue is you took the page out of the PTE it belongs to, which
makes it orphaned and unlocatable by the rest of the mm?

Ideally this would leave the PTE in place so everything continues to
work, just disable CPU access to it.

Maybe some kind of special swap entry?

I also don't much like the use of ZONE_DEVICE here, that should only
be used for actual device memory, not as a temporary proxy for CPU
pages.. Having two struct pages refer to the same physical memory is
pretty ugly.

> The normal solution of registering an MMU notifier to unpin the page when it 
> needs to be moved also doesn't work as the CPU page tables now point to the
> device-private page and hence the migration code won't call any invalidate 
> notifiers for the CPU page.

The fact the page is lost from the MM seems to be the main issue here.

> Yes, I would like to avoid the long term pin constraints as well if possible I 
> just haven't found a solution yet. Are you suggesting it might be possible to 
> add a callback in the page migration logic to specially deal with moving these 
> pages?

How would migration even find the page?

Jason
_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  1:07 Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 1/9] mm/migrate.c: Always allow device private pages to migrate Alistair Popple
2021-02-09 13:39   ` Jason Gunthorpe
2021-02-10  3:40     ` Alistair Popple
2021-02-10 12:56       ` Jason Gunthorpe
2021-02-09  1:07 ` [Nouveau] [PATCH 2/9] mm/migrate.c: Allow pfn flags to be passed to migrate_vma_setup() Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 3/9] mm/migrate: Add a unmap and pin migration mode Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 4/9] Documentation: Add unmap and pin to HMM Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 5/9] hmm-tests: Add test for unmap and pin Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 6/9] nouveau/dmem: Only map migrating pages Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 7/9] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 8/9] nouveau/dmem: Add support for multiple page types Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 9/9] nouveau/svm: Implement atomic SVM access Alistair Popple
2021-02-09 10:27 ` [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau Daniel Vetter
2021-02-09 12:57   ` Alistair Popple
2021-02-09 13:35     ` Jason Gunthorpe [this message]
2021-02-09 13:39       ` Daniel Vetter
2021-02-09 13:44         ` Jason Gunthorpe
2021-02-09 21:17       ` Jerome Glisse
2021-02-10 17:56         ` Jason Gunthorpe
2021-02-09 13:37     ` Daniel Vetter
2021-02-09 20:53       ` John Hubbard
2021-02-10 12:59         ` Daniel Vetter
2021-02-11  2:26           ` John Hubbard
2021-02-10 17:59         ` Jason Gunthorpe
2021-02-11  7:55           ` Christoph Hellwig
2021-02-17 23:00             ` Alistair Popple

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210209133520.GB4718@ziepe.ca \
    --to=jgg@ziepe.ca \
    --cc=akpm@linux-foundation.org \
    --cc=apopple@nvidia.com \
    --cc=bskeggs@redhat.com \
    --cc=daniel@ffwll.ch \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=kvm-ppc@vger.kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=nouveau@lists.freedesktop.org \
    --cc=rcampbell@nvidia.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Nouveau Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/nouveau/0 nouveau/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 nouveau nouveau/ https://lore.kernel.org/nouveau \
		nouveau@lists.freedesktop.org
	public-inbox-index nouveau

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.freedesktop.lists.nouveau


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git