From: Christopher Lameter <cl@linux.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Jan Kara <jack@suse.cz>,
john.hubbard@gmail.com, Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
Dan Williams <dan.j.williams@intel.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-rdma <linux-rdma@vger.kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 5/6] mm: track gup pages with page->dma_pinned_* fields
Date: Tue, 3 Jul 2018 17:08:12 +0000 [thread overview]
Message-ID: <01000164611dacae-5ac25e48-b845-43ef-9992-fc1047d8e0a0-000000@email.amazonses.com> (raw)
In-Reply-To: <f01666d5-8da1-7bea-adfb-c3571a54587a@nvidia.com>
On Mon, 2 Jul 2018, John Hubbard wrote:
> > If you establish a reference to a page then increase the page count. If
> > the reference is a dma pin action also then increase the pinned count.
> >
> > That way you know how many of the references to the page are dma
> > pins and you can correctly manage the state of the page if the dma pins go
> > away.
> >
>
> I think this sounds like what this patch already does, right? See:
> __put_page_for_pinned_dma(), __get_page_for_pinned_dma(), and
> pin_page_for_dma(). The locking seems correct to me, but I suspect it's
> too heavyweight for such a hot path. But without adding a new put_user_page()
> call, that was the best I could come up with.
When I saw the patch it looked like you were avoiding to increment the
page->count field.
> What I'm hearing now from Jan and Michal is that the desired end result is
> a separate API call, put_user_pages(), so that we can explicitly manage
> these pinned pages.
Certainly a good approach.
next prev parent reply other threads:[~2018-07-03 17:08 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-02 0:56 [PATCH v2 0/6] mm/fs: gup: don't unmap or drop filesystem buffers john.hubbard
2018-07-02 0:56 ` [PATCH v2 1/6] mm: get_user_pages: consolidate error handling john.hubbard
2018-07-02 10:17 ` Jan Kara
2018-07-02 21:34 ` John Hubbard
2018-07-02 0:56 ` [PATCH v2 2/6] mm: introduce page->dma_pinned_flags, _count john.hubbard
2018-07-02 0:56 ` [PATCH v2 3/6] mm: introduce zone_gup_lock, for dma-pinned pages john.hubbard
2018-07-02 0:56 ` [PATCH v2 4/6] mm/fs: add a sync_mode param for clear_page_dirty_for_io() john.hubbard
2018-07-02 2:11 ` kbuild test robot
2018-07-02 4:40 ` John Hubbard
2018-07-02 2:47 ` kbuild test robot
2018-07-02 4:40 ` John Hubbard
2018-07-02 0:56 ` [PATCH v2 5/6] mm: track gup pages with page->dma_pinned_* fields john.hubbard
2018-07-02 2:11 ` kbuild test robot
2018-07-02 2:58 ` kbuild test robot
2018-07-02 5:05 ` John Hubbard
2018-07-02 9:53 ` Jan Kara
2018-07-02 20:43 ` John Hubbard
2018-07-03 0:08 ` Christopher Lameter
2018-07-03 4:30 ` John Hubbard
2018-07-03 17:08 ` Christopher Lameter [this message]
2018-07-03 17:36 ` John Hubbard
2018-07-03 17:48 ` Christopher Lameter
2018-07-03 18:48 ` John Hubbard
2018-07-04 10:43 ` Jan Kara
2018-07-05 14:17 ` Christopher Lameter
2018-07-09 13:49 ` Jan Kara
2018-07-02 0:56 ` [PATCH v2 6/6] mm: page_mkclean, ttu: handle pinned pages john.hubbard
2018-07-02 10:15 ` Jan Kara
2018-07-02 21:07 ` John Hubbard
2018-07-02 5:54 ` [PATCH v2 0/6] mm/fs: gup: don't unmap or drop filesystem buffers John Hubbard
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