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

John Hubbard
2020-05-22T05:19:37Z

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/159008745422.32320.5724805750977048669@build.alporthouse.com

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
--
2.26.2