From: Ira Weiny <ira.weiny@intel.com>
To: Jan Kara <jack@suse.cz>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Dave Chinner" <david@fromorbit.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Jérôme Glisse" <jglisse@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-rdma@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()
Date: Thu, 15 Aug 2019 10:32:37 -0700 [thread overview]
Message-ID: <20190815173237.GA30924@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20190815133510.GA21302@quack2.suse.cz>
On Thu, Aug 15, 2019 at 03:35:10PM +0200, Jan Kara wrote:
> On Thu 15-08-19 15:26:22, Jan Kara wrote:
> > On Wed 14-08-19 20:01:07, John Hubbard wrote:
> > > On 8/14/19 5:02 PM, John Hubbard wrote:
> > >
> > > Hold on, I *was* forgetting something: this was a two part thing, and
> > > you're conflating the two points, but they need to remain separate and
> > > distinct. There were:
> > >
> > > 1. FOLL_PIN is necessary because the caller is clearly in the use case that
> > > requires it--however briefly they might be there. As Jan described it,
> > >
> > > "Anything that gets page reference and then touches page data (e.g.
> > > direct IO) needs the new kind of tracking so that filesystem knows
> > > someone is messing with the page data." [1]
> >
> > So when the GUP user uses MMU notifiers to stop writing to pages whenever
> > they are writeprotected with page_mkclean(), they don't really need page
> > pin - their access is then fully equivalent to any other mmap userspace
> > access and filesystem knows how to deal with those. I forgot out this case
> > when I wrote the above sentence.
> >
> > So to sum up there are three cases:
> > 1) DIO case - GUP references to pages serving as DIO buffers are needed for
> > relatively short time, no special synchronization with page_mkclean() or
> > munmap() => needs FOLL_PIN
> > 2) RDMA case - GUP references to pages serving as DMA buffers needed for a
> > long time, no special synchronization with page_mkclean() or munmap()
> > => needs FOLL_PIN | FOLL_LONGTERM
> > This case has also a special case when the pages are actually DAX. Then
> > the caller additionally needs file lease and additional file_pin
> > structure is used for tracking this usage.
> > 3) ODP case - GUP references to pages serving as DMA buffers, MMU notifiers
> > used to synchronize with page_mkclean() and munmap() => normal page
> > references are fine.
>
> I want to add that I'd like to convert users in cases 1) and 2) from using
> GUP to using differently named function. Users in case 3) can stay as they
> are for now although ultimately I'd like to denote such use cases in a
> special way as well...
>
Ok just to make this clear I threw up my current tree with your patches here:
https://github.com/weiny2/linux-kernel/commits/mmotm-rdmafsdax-b0-v4
I'm talking about dropping the final patch:
05fd2d3afa6b rdma/umem_odp: Use vaddr_pin_pages_remote() in ODP
The other 2 can stay. I split out the *_remote() call. We don't have a user
but I'll keep it around for a bit.
This tree is still WIP as I work through all the comments. So I've not changed
names or variable types etc... Just wanted to settle this.
Ira
next prev parent reply other threads:[~2019-08-15 17:32 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 1:50 [RFC PATCH 0/2] mm/gup: introduce vaddr_pin_pages_remote(), FOLL_PIN john.hubbard
2019-08-12 1:50 ` [RFC PATCH 1/2] mm/gup: introduce FOLL_PIN flag for get_user_pages() john.hubbard
2019-08-12 1:50 ` [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote() john.hubbard
2019-08-12 22:03 ` Ira Weiny
2019-08-12 22:21 ` John Hubbard
2019-08-12 23:49 ` Ira Weiny
2019-08-13 0:07 ` John Hubbard
2019-08-13 21:08 ` Ira Weiny
2019-08-14 0:51 ` John Hubbard
2019-08-14 0:56 ` John Hubbard
2019-08-14 23:50 ` Ira Weiny
2019-08-15 0:02 ` John Hubbard
2019-08-15 3:01 ` John Hubbard
2019-08-15 13:26 ` Jan Kara
2019-08-15 13:35 ` Jan Kara
2019-08-15 14:51 ` Jason Gunthorpe
2019-08-15 17:32 ` Ira Weiny [this message]
2019-08-15 17:41 ` John Hubbard
2019-08-16 2:14 ` John Hubbard
2019-08-16 15:41 ` Jan Kara
2019-08-16 18:33 ` Ira Weiny
2019-08-16 18:50 ` John Hubbard
2019-08-16 21:59 ` Ira Weiny
2019-08-16 22:36 ` John Hubbard
2019-08-16 8:47 ` Vlastimil Babka
2019-08-16 15:44 ` Jan Kara
2019-08-16 15:52 ` Jerome Glisse
2019-08-16 16:13 ` Jan Kara
2019-08-16 16:31 ` Jason Gunthorpe
2019-08-16 16:54 ` Jerome Glisse
2019-08-16 17:04 ` Jason Gunthorpe
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