On 1/24/21 3:18 PM, John Hubbard wrote:
On 1/21/21 7:37 PM, Pavel Tatashin wrote:
When pages are pinned they can be faulted in userland and migrated, and
they can be faulted right in kernel without migration.
In either case, the pinned pages must end-up being pinnable (not movable).
Add a new test to gup_test, to help verify that the gup/pup
(get_user_pages() / pin_user_pages()) behavior with respect to pinnable
and movable pages is reasonable and correct. Specifically, provide a
way to:
1) Verify that only "pinnable" pages are pinned. This is checked
automatically for you.
2) Verify that gup/pup performance is reasonable. This requires
comparing benchmarks between doing gup/pup on pages that have been
pre-faulted in from user space, vs. doing gup/pup on pages that are not
faulted in until gup/pup time (via FOLL_TOUCH). This decision is
controlled with the new -z command line option.
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
mm/gup_test.c | 6 ++++++
tools/testing/selftests/vm/gup_test.c | 23 +++++++++++++++++++----
2 files changed, 25 insertions(+), 4 deletions(-)
This also looks good. I do see the WARN_ON_ONCE firing in
internal_get_user_pages_fast(), when running with *only* the new -z
option.
I'll poke around the rest of the patchset and see if that is expected
and normal, but either way the test code itself looks correct and seems
The warning that is firing in internal_get_user_pages_fast() is:
if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
FOLL_FORCE | FOLL_PIN | FOLL_GET |
FOLL_FAST_ONLY)))
return -EINVAL;
...OK, so this is because "./gup_test -z" invokes get_user_pages_fast(),
which so far does not allow passing in FOLL_TOUCH. Probably because there
is nothing "fast" about touching and possibly faulting in pages. :)
So, again, the test code still looks correct, even though it's possible
to pass in options that run into things that are rejected by gup.c
thanks,
--
John Hubbard
NVIDIA
