From: Dan Williams <dan.j.williams@intel.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jan Kara" <jack@suse.cz>, "Jason Gunthorpe" <jgg@ziepe.ca>,
"Jens Axboe" <axboe@kernel.dk>,
"Jérôme Glisse" <jglisse@redhat.com>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
"Linux MM" <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH 2/2] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
Date: Mon, 18 Nov 2019 08:57:01 -0800 [thread overview]
Message-ID: <CAPcyv4ganBBR61ZEwGHOoA+FeAdSY8rWzTCNM=zhnfn27KOafw@mail.gmail.com> (raw)
In-Reply-To: <20191118070826.GB3099@infradead.org>
On Sun, Nov 17, 2019 at 11:09 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Nov 14, 2019 at 04:11:34PM -0800, John Hubbard wrote:
> > An upcoming patch changes and complicates the refcounting and
> > especially the "put page" aspects of it. In order to keep
> > everything clean, refactor the devmap page release routines:
> >
> > * Rename put_devmap_managed_page() to page_is_devmap_managed(),
> > and limit the functionality to "read only": return a bool,
> > with no side effects.
> >
> > * Add a new routine, put_devmap_managed_page(), to handle checking
> > what kind of page it is, and what kind of refcount handling it
> > requires.
> >
> > * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
> > and limit the functionality to unconditionally freeing a devmap
> > page.
> >
> > This is originally based on a separate patch by Ira Weiny, which
> > applied to an early version of the put_user_page() experiments.
> > Since then, Jérôme Glisse suggested the refactoring described above.
>
> I can't say I'm a big fan of this as it adds a lot more inlined
> code to put_page, which has a lot of callsites. Can't we instead
> try to figure out a way to move away from the off by one refcounting?
That might be possible. David and I are discussing a pfn_online()
helper that might be a replacement for keeping ZONE_DEVICE pages out
of the page allocator rather than keeping their reference count
elevated.
prev parent reply other threads:[~2019-11-18 16:57 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-15 0:11 [PATCH 0/2] mm: devmap: page-freeing related cleanups John Hubbard
2019-11-15 0:11 ` [PATCH 1/2] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-11-18 7:04 ` Christoph Hellwig
2019-11-15 0:11 ` [PATCH 2/2] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-15 9:48 ` Jan Kara
2019-11-15 16:41 ` Dan Williams
2019-11-18 7:08 ` Christoph Hellwig
2019-11-18 16:57 ` Dan Williams [this message]
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