Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Vlastimil Babka <vbabka@suse.cz>
To: Jan Kara <jack@suse.cz>, John Hubbard <jhubbard@nvidia.com>
Cc: "Ira Weiny" <ira.weiny@intel.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: Fri, 16 Aug 2019 10:47:21 +0200
Message-ID: <0d6797d8-1e04-1ebe-80a7-3d6895fe71b0@suse.cz> (raw)
In-Reply-To: <20190815133510.GA21302@quack2.suse.cz>

On 8/15/19 3:35 PM, Jan Kara wrote:
>> 
>> 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.

IMHO the munlock lesson told us about another one, that's in the end equivalent
to 3)

4) pinning for struct page manipulation only => 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...

So after 1/2/3 is renamed/specially denoted, only 4) keeps the current interface?

> 								Honza
> 



  parent reply index

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
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 [this message]
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

Reply instructions:

You may reply publically 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=0d6797d8-1e04-1ebe-80a7-3d6895fe71b0@suse.cz \
    --to=vbabka@suse.cz \
    --cc=akpm@linux-foundation.org \
    --cc=dan.j.williams@intel.com \
    --cc=david@fromorbit.com \
    --cc=hch@infradead.org \
    --cc=ira.weiny@intel.com \
    --cc=jack@suse.cz \
    --cc=jgg@ziepe.ca \
    --cc=jglisse@redhat.com \
    --cc=jhubbard@nvidia.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-rdma@vger.kernel.org \
    /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

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/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 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org linux-mm@archiver.kernel.org
	public-inbox-index linux-mm


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


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