[v2,0/4] mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()

Message

John Hubbard May 22, 2020, 5:19 a.m. UTC

The purpose of posting this series is to launch a test in the
intel-gfx-ci tree. (The patches have already been merged into Andrew's
linux-mm tree.)

This applies to today's linux.git (note the base-commit tag at the
bottom).

Changes since V1:

* Fixed a bug in the refactoring patch: added FOLL_FAST_ONLY to the
  list of gup_flags *not* to WARN() on. This lead to a failure in the
  first intel-gfx-ci test run [1].

[1] https://lore.kernel.org/r/[e-mail]

Original cover letter:

This needs to go through Andrew's -mm tree, due to adding a new gup.c
routine. However, I would really love to have some testing from the
drm/i915 folks, because I haven't been able to run-time test that part
of it.

Otherwise, though, the series has passed my basic run time testing:
some LTP tests, some xfs and etx4 non-destructive xfstests, and an
assortment of other smaller ones: vm selftests, io_uring_register, a
few more. But that's only on one particular machine. Also, cross-compile
tests for half a dozen arches all pass.

Details:

In order to convert the drm/i915 driver from get_user_pages() to
pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was
required. That led to refactoring __get_user_pages_fast(), with the
following goals:

1) As above: provide a pin_user_pages*() routine for drm/i915 to call,
   in place of __get_user_pages_fast(),

2) Get rid of the gup.c duplicate code for walking page tables with
   interrupts disabled. This duplicate code is a minor maintenance
   problem anyway.

3) Make it easy for an upcoming patch from Souptick, which aims to
   convert __get_user_pages_fast() to use a gup_flags argument, instead
   of a bool writeable arg.  Also, if this series looks good, we can
   ask Souptick to change the name as well, to whatever the consensus
   is. My initial recommendation is: get_user_pages_fast_only(), to
   match the new pin_user_pages_only().

John Hubbard (4):
  mm/gup: move __get_user_pages_fast() down a few lines in gup.c
  mm/gup: refactor and de-duplicate gup_fast() code
  mm/gup: introduce pin_user_pages_fast_only()
  drm/i915: convert get_user_pages() --> pin_user_pages()

 drivers/gpu/drm/i915/gem/i915_gem_userptr.c |  22 +--
 include/linux/mm.h                          |   3 +
 mm/gup.c                                    | 153 ++++++++++++--------
 3 files changed, 109 insertions(+), 69 deletions(-)


base-commit: 051143e1602d90ea71887d92363edd539d411de5

Comments

John Hubbard May 23, 2020, 10:33 p.m. UTC | #1

On 2020-05-23 02:41, Chris Wilson wrote:
> Quoting John Hubbard (2020-05-22 06:19:27)
>> The purpose of posting this series is to launch a test in the
>> intel-gfx-ci tree. (The patches have already been merged into Andrew's
>> linux-mm tree.)
>>
>> This applies to today's linux.git (note the base-commit tag at the
>> bottom).
>>
>> Changes since V1:
>>
>> * Fixed a bug in the refactoring patch: added FOLL_FAST_ONLY to the
>>    list of gup_flags *not* to WARN() on. This lead to a failure in the
>>    first intel-gfx-ci test run [1].
>>
>> [1] https://lore.kernel.org/r/[e-mail]
> 
> Ran this through our CI, warn and subsequent lockup were gone. That
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Yea! Thanks again for these test runs. I really don't like posting
patches that I can't run-time test, but this CI system mitigates
that pretty well.


> lockup is worrying me now, but that doesn't seem to be an issue from
> this series.


I do think it's worth following up on. And it seems like it would be
very easy to repro: just hack in a forced failure at the call site of
pin_user_pages_fast_only(), and follow the breadcrumbs.


> 
> The i915 changes were simple enough, I would have computed the pin flags
> just once (since the readonly bit is static, that would be interesting
> if that was allowed to change mid gup :)
> Reviewed-by: Chris Wilson <[e-mail]>
> -Chris
> 

Thanks for the review! And if lifting that check up higher in the call
stack is desired, I'm all in favor of that being done...in a separate
patch. :)

I'm trying to keep a very light touch when converting these call sites.

thanks,