On 07/23/2015 10:17 AM, Eric B Munson wrote:
On Thu, 23 Jul 2015, Mike Kravetz wrote:
On 07/23/2015 08:17 AM, Eric B Munson wrote:
On Wed, 22 Jul 2015, Mike Kravetz wrote:
On 07/22/2015 03:30 PM, Andrew Morton wrote:
On Wed, 22 Jul 2015 15:19:54 -0700 Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
I didn't know that libhugetlbfs has tests. I wonder if that makes
tools/testing/selftests/vm's hugetlbfstest harmful?
Why harmful? Redundant, maybe(?).
The presence of the in-kernel tests will cause people to add stuff to
them when it would be better if they were to apply that effort to
making libhugetlbfs better. Or vice versa.
Mike's work is an example. Someone later makes a change to hugetlbfs, runs
the kernel selftest and says "yay, everything works", unaware that they
just broke fallocate support.
Does anyone even use selftests for
hugetlbfs regression testing? Lets see, we also have these:
- hugepage-{mmap,shm}.c
- map_hugetlb.c
There's probably a lot of room for improvement here.
selftests is a pretty scrappy place. It's partly a dumping ground for
things so useful test code doesn't just get lost and bitrotted. Partly
a framework so people who add features can easily test them. Partly to
provide tools to architecture maintainers when they wire up new
syscalls and the like.
Unless there's some good reason to retain the hugetlb part of
selftests, I'm thinking we should just remove it to avoid
distracting/misleading people. Or possibly move the libhugetlbfs test
code into the kernel tree and maintain it there.
Adding Eric as he is the libhugetlbfs maintainer.
I think removing the hugetlb selftests in the kernel and pointing
people to libhugetlbfs is the way to go. From a very quick scan
of the selftests, I would guess libhugetlbfs covers everything
in those tests.
I'm willing to verify the testing provided by selftests is included
in libhugetlbfs, and remove selftests if that is the direction we
want to take.
I would rather see the test suite stay in the library, there are a
number of tests that rely on infrastructure in the library that is not
available in selftests.
I am happy to help with any tests that need to be added/modified in the
library to cover.
I thought about this some more and think there are two distinct
groups of users that should be considered.
1) Application developers who simply want to use hugetlb
2) Kernel developers who are modifying hugetlb related code
The application developers will mostly want information in the
man pages, hugetlbpage.txt and hugetlb selftest programs to use
as sample code to get started. They can also use libhugetlbfs
man pages/library if they desire. Because of this, I do not
really want to remove the hugetlb selftest programs. There are
no equivalent simple stand alone programs in libhugetlbfs.
Kernel developers would be more concerned about introducing
regressions. The selftest programs are of limited use for this
purpose. The libhugetlbfs test suite is much more suited for
regression testing.
With this in mind, I suggest:
- Keep the mmap man page reference to Documentation/vm/hugetlbpage.txt
- Small modification to hugetlbpage.txt saying the selftest code is
good for application development examples. And, kernel developers
should use libhugetlbfs test suite for regression testing. In any
case, the sourceforge URL for libhugetlbfs is no longer valid and
needs to be updated.
- Modify the run_vmtests selftest script to print out a message saying
libhugetlbfs should be used for hugetlb regression testing. This
would help catch people who might think the few selftests are
sufficient.
Thoughts?
There are a number of tests in the libhugetlbfs suite that cover kernel
problems, are you suggesting that we move all these tests out of
libhugetlbfs and into selftests? I don't think we should separate the
responsibility for testing kernel regressions so where ever they end up,
they should all be together. The libhugetlbfs suite has some nice
features for setting up the test environment (consider that a plug to
move tests in that direction).
No, not suggesting we move anything out of libhugetlbfs. I believe
that should be the primary test suite for hugetlb.
However, the few programs in selftest do provide some value IMO.
They are examples of hugetlb usage without any of the libhugetlbfs
infrastructure present. Ideally, there would be some place to put
this sample code. I can not think of an ideal location.
--
Mike Kravetz
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