linux/drivers/media/v4l2-core
Ira Weiny 932f4a630a mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM
Pach series "Add FOLL_LONGTERM to GUP fast and use it".

HFI1, qib, and mthca, use get_user_pages_fast() due to its performance
advantages.  These pages can be held for a significant time.  But
get_user_pages_fast() does not protect against mapping FS DAX pages.

Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which
retains the performance while also adding the FS DAX checks.  XDP has also
shown interest in using this functionality.[1]

In addition we change get_user_pages() to use the new FOLL_LONGTERM flag
and remove the specialized get_user_pages_longterm call.

[1] https://lkml.org/lkml/2019/3/19/939

"longterm" is a relative thing and at this point is probably a misnomer.
This is really flagging a pin which is going to be given to hardware and
can't move.  I've thought of a couple of alternative names but I think we
have to settle on if we are going to use FL_LAYOUT or something else to
solve the "longterm" problem.  Then I think we can change the flag to a
better name.

Secondly, it depends on how often you are registering memory.  I have
spoken with some RDMA users who consider MR in the performance path...
For the overall application performance.  I don't have the numbers as the
tests for HFI1 were done a long time ago.  But there was a significant
advantage.  Some of which is probably due to the fact that you don't have
to hold mmap_sem.

Finally, architecturally I think it would be good for everyone to use
*_fast.  There are patches submitted to the RDMA list which would allow
the use of *_fast (they reworking the use of mmap_sem) and as soon as they
are accepted I'll submit a patch to convert the RDMA core as well.  Also
to this point others are looking to use *_fast.

As an aside, Jasons pointed out in my previous submission that *_fast and
*_unlocked look very much the same.  I agree and I think further cleanup
will be coming.  But I'm focused on getting the final solution for DAX at
the moment.

This patch (of 7):

This patch starts a series which aims to support FOLL_LONGTERM in
get_user_pages_fast().  Some callers who would like to do a longterm (user
controlled pin) of pages with the fast variant of GUP for performance
purposes.

Rather than have a separate get_user_pages_longterm() call, introduce
FOLL_LONGTERM and change the longterm callers to use it.

This patch does not change any functionality.  In the short term
"longterm" or user controlled pins are unsafe for Filesystems and FS DAX
in particular has been blocked.  However, callers of get_user_pages_fast()
were not "protected".

FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it
requires vmas to determine if DAX is in use.

NOTE: In merging with the CMA changes we opt to change the
get_user_pages() call in check_and_migrate_cma_pages() to a call of
__get_user_pages_locked() on the newly migrated pages.  This makes the
code read better in that we are calling __get_user_pages_locked() on the
pages before and after a potential migration.

As a side affect some of the interfaces are cleaned up but this is not the
primary purpose of the series.

In review[1] it was asked:

<quote>
> This I don't get - if you do lock down long term mappings performance
> of the actual get_user_pages call shouldn't matter to start with.
>
> What do I miss?

A couple of points.

First "longterm" is a relative thing and at this point is probably a
misnomer.  This is really flagging a pin which is going to be given to
hardware and can't move.  I've thought of a couple of alternative names
but I think we have to settle on if we are going to use FL_LAYOUT or
something else to solve the "longterm" problem.  Then I think we can
change the flag to a better name.

Second, It depends on how often you are registering memory.  I have spoken
with some RDMA users who consider MR in the performance path...  For the
overall application performance.  I don't have the numbers as the tests
for HFI1 were done a long time ago.  But there was a significant
advantage.  Some of which is probably due to the fact that you don't have
to hold mmap_sem.

Finally, architecturally I think it would be good for everyone to use
*_fast.  There are patches submitted to the RDMA list which would allow
the use of *_fast (they reworking the use of mmap_sem) and as soon as they
are accepted I'll submit a patch to convert the RDMA core as well.  Also
to this point others are looking to use *_fast.

As an asside, Jasons pointed out in my previous submission that *_fast and
*_unlocked look very much the same.  I agree and I think further cleanup
will be coming.  But I'm focused on getting the final solution for DAX at
the moment.

</quote>

[1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965

[ira.weiny@intel.com: v3]
  Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com
Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com
Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Mike Marshall <hubcap@omnibond.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 09:47:45 -07:00
..
Kconfig media: Kconfig files: use the right help coding style 2019-03-20 06:47:51 -04:00
Makefile media: v4l2-core: get rid of videobuf-dvb 2018-05-04 10:57:31 -04:00
tuner-core.c media: v4l2-mc: get rid of global pad indexes 2018-09-17 13:16:19 -04:00
v4l2-async.c media: v4l2: async: remove locking when initializing async notifier 2018-12-05 06:51:28 -05:00
v4l2-clk.c media: Convert to using %pOF instead of full_name 2017-08-20 08:20:20 -04:00
v4l2-common.c media: v4l2-common: add bayer formats in v4l2_format_info 2019-04-22 10:33:45 -04:00
v4l2-compat-ioctl32.c Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
v4l2-ctrls.c media: v4l: add I / P frame min max QP definitions 2019-04-22 10:25:36 -04:00
v4l2-dev.c media: v4l: Add support for V4L2_BUF_TYPE_META_OUTPUT 2018-12-14 05:10:48 -05:00
v4l2-device.c media: v4l2-subdev: add release() internal op 2019-03-19 13:24:28 -04:00
v4l2-dv-timings.c media: hdmi.h: rename ADOBE_RGB to OPRGB and ADOBE_YCC to OPYCC 2018-09-24 09:28:41 -04:00
v4l2-event.c media: v4l2-event: keep track of the timestamp in ns 2019-02-07 12:11:15 -05:00
v4l2-fh.c media: v4l: event: Prevent freeing event subscriptions while accessed 2018-10-03 06:32:51 -04:00
v4l2-flash-led-class.c media: use strscpy() instead of strlcpy() 2018-09-11 13:32:17 -04:00
v4l2-fwnode.c media: v4l2-fwnode: Add a deprecation note in the old ACPI parsing example 2019-03-20 06:37:55 -04:00
v4l2-ioctl.c media: v4l2-ioctl.c: add V4L2_PIX_FMT_FWHT_STATELESS to v4l_fill_fmtdesc 2019-03-25 14:02:57 -04:00
v4l2-mc.c media: v4l2-mc: add print messages when media graph fails 2018-09-17 13:16:19 -04:00
v4l2-mem2mem.c media: v4l2-mem2mem: Correct return type for mem2mem buffer helpers 2019-02-18 15:32:14 -05:00
v4l2-subdev.c media: v4l2-subdev: handle module refcounting here 2019-03-19 13:29:37 -04:00
v4l2-trace.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
videobuf-core.c media: v4l2-core: fix several typos 2019-03-01 09:44:17 -05:00
videobuf-dma-contig.c media: v4l2-core: fix several typos 2019-03-01 09:44:17 -05:00
videobuf-dma-sg.c mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM 2019-05-14 09:47:45 -07:00
videobuf-vmalloc.c media: v4l2-core: fix several typos 2019-03-01 09:44:17 -05:00