Re: [PATCH v5 8/8] mm: huge_memory: enable debugfs to split huge pages to any order.

[Zi Yan <ziy@nvidia.com>]

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On 1 Mar 2024, at 8:09, Ryan Roberts wrote:

> On 01/03/2024 12:52, Zi Yan wrote:
>> On 1 Mar 2024, at 5:33, Ryan Roberts wrote:
>>
>>> On 01/03/2024 09:51, Aishwarya TCV wrote:
>>>>
>>>>
>>>> On 26/02/2024 20:55, Zi Yan wrote:
>>>>> From: Zi Yan <ziy@nvidia.com>
>>>>>
>>>>> It is used to test split_huge_page_to_list_to_order for pagecache THPs.
>>>>> Also add test cases for split_huge_page_to_list_to_order via both
>>>>> debugfs.
>>>>>
>>>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>>> ---
>>>>>  mm/huge_memory.c                              |  34 ++++--
>>>>>  .../selftests/mm/split_huge_page_test.c       | 115 +++++++++++++++++-
>>>>>  2 files changed, 131 insertions(+), 18 deletions(-)
>>>>>
>>>>
>>>> Hi Zi,
>>>>
>>>> When booting the kernel against next-master(20240228)with Arm64 on
>>>> Marvell Thunder X2 (TX2), the kselftest-mm test 'split_huge_page_test'
>>>> is failing in our CI (with rootfs over NFS). I can send the full logs if
>>>> required.
>>>
>>> Just to add, I took a quick eyeball and I think there a couple of potential issues:
>>>
>>>   - In create_pagecache_thp_and_fd() you do *fd = open(testfile, O_CREAT ...);
>>>     where testfile is /mnt/thp_fs/testfile. So if /mnt/thp_fs doesn't exist,
>>>     then the open will fail I think? I'm pretty sure that's what's happening on
>>>     our CI. Suggest the test needs to setup this dir itself. Is thp_fs a mounted
>>>     fs or just a dir? If the latter can you just mktemp()?
>>
>> The former. the page cache folio split tests require a file system supporting
>> large folio and I used XFS.
>
> OK got it.
>
>>
>>>   - Later in create_pagecache_thp_and_fd() you fail the test if you don't have a
>>>     filesystem that supports large folios. Can we turn that into a skip? That
>>>     would reduce noise on the CI.
>>
>> I can do that. But is this a new requirement that self tests have to be finish
>> in CI/CD environment? Can you provide a guideline for it?
>
> I'm not sure what's written down, but certainly anyone should be able to run the
> selftests with as little knowledge as possible, and they should only fail if
> they detect a real problem. By convention a test should be skipped if the
> environment (or kernel) isn't compatible. There are lots of examples of that in
> mm selftests (just grep ksft_test_result_skip). mm selftests also has
> run_vmtests.sh which does a lot of environment setup (e.g. reserving hugetlb
> pages, etc) before actually running the tests.

Got it. I will send a fixup to skip the page cache split test when the mount
is not ready, then send a separate patch to set up XFS in run_vmtests.sh and
pass it to this test.

>
>> Since I always assume
>> selftests are just ran by human who can set up environment.
>
> I believe kernelci have been running mm skeftests on x86 for a long time. We
> have started running them against arm64 on our CI for the last couple of months
> and it had found a number of real issues in the kernel in -next, so this is
> helping find and fix things early. So there is definitely benefit to keeping
> these tests clean and robust.

Got it. Make sense.

>
>> In addition, I do
>> not think it is realistic to make the test file to set up all the environment,
>> since everyone's machine is different. It is much easier to make the CI/CD
>> environment to make the mount.
>
> That's reasonable, but then the requirements should be documented and you
> probably would want to be able to optionally pass the mount on the command line.

Will do.

Thank you for the explanation.

>>>
>>> Thanks,
>>> Ryan
>>>
>>>>
>>>> A bisect (full log below) identified this patch as introducing the
>>>> failure. Bisected it on the tag "next-20240228" at repo
>>>> "https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git".
>>>>
>>>> This works fine on  Linux version 6.8.0-rc6
>>>>
>>>>
>>>> Sample log from failure against run on TX2:
>>>> ------
>>>> 07:17:34.056125  # # ------------------------------
>>>> 07:17:34.056543  # # running ./split_huge_page_test
>>>> 07:17:34.056839  # # ------------------------------
>>>> 07:17:34.057114  # # TAP version 13
>>>> 07:17:34.058564  # # 1..12
>>>> 07:17:34.156822  # # ok 1 Split huge pages successful
>>>> 07:17:34.214074  # # ok 2 Split PTE-mapped huge pages successful
>>>> 07:17:34.215630  # # # Please enable pr_debug in
>>>> split_huge_pages_in_file() for more info.
>>>> 07:17:34.225503  # # # Please check dmesg for more information
>>>> 07:17:34.225862  # # ok 3 File-backed THP split test done
>>>> 07:17:34.236944  # # Bail out! Failed to create a file at /mnt/thp_fs#
>>>> Planned tests != run tests (12 != 3)
>>>> 07:17:34.237307  # # # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
>>>> 07:17:34.237620  # # [FAIL]
>>>> 07:17:34.246430  # not ok 51 split_huge_page_test # exit=1
>>>>
>>>>
>>>> Bisect log:
>>>> ------
>>>> git bisect start
>>>> # good: [d206a76d7d2726f3b096037f2079ce0bd3ba329b] Linux 6.8-rc6
>>>> git bisect good d206a76d7d2726f3b096037f2079ce0bd3ba329b
>>>> # bad: [20af1ca418d2c0b11bc2a1fe8c0c88f67bcc2a7e] Add linux-next
>>>> specific files for 20240228
>>>> git bisect bad 20af1ca418d2c0b11bc2a1fe8c0c88f67bcc2a7e
>>>> # bad: [1322f1801e59dddce10591d602d246c1bf49990c] Merge branch 'main' of
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git
>>>> git bisect bad 1322f1801e59dddce10591d602d246c1bf49990c
>>>> # bad: [a82f70041487790b7b09fe4bb45436e1b57021d3] Merge branch 'dev' of
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git
>>>> git bisect bad a82f70041487790b7b09fe4bb45436e1b57021d3
>>>> # bad: [ce90480b9352ba2bebe8946dad9223e3f24c6e9a] Merge branch
>>>> 'for-next' of
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap.git
>>>> git bisect bad ce90480b9352ba2bebe8946dad9223e3f24c6e9a
>>>> # bad: [5daac92ed3881fd0c656478a301a4e1d124100ee] Merge branch
>>>> 'mm-everything' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
>>>> git bisect bad 5daac92ed3881fd0c656478a301a4e1d124100ee
>>>> # good: [acc2643d9e988c63dd4629a9af380ad9ac69c54a] Merge branch
>>>> 'mm-stable' into mm-unstable
>>>> git bisect good acc2643d9e988c63dd4629a9af380ad9ac69c54a
>>>> # good: [0294de8fe7d7c1a7eddc979cbf4c1886406e36b7] Merge branch 'fixes'
>>>> of git://git.kernel.org/pub/scm/linux/kernel/git/sre/linux-power-supply.git
>>>> git bisect good 0294de8fe7d7c1a7eddc979cbf4c1886406e36b7
>>>> # good: [83e0c8f0e777a1ef0977b2f8189101765703b32d] Merge branch
>>>> 'mm-nonmm-stable' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
>>>> git bisect good 83e0c8f0e777a1ef0977b2f8189101765703b32d
>>>> # good: [a739cbe236e0dd3b6ff26a01fa1d31c73d4fac93] mm: memcg: make memcg
>>>> huge page split support any order split
>>>> git bisect good a739cbe236e0dd3b6ff26a01fa1d31c73d4fac93
>>>> # bad: [efb520aa333b2f11daaaaa13f4a598b5ae4ae823] mm: allow non-hugetlb
>>>> large folios to be batch processed
>>>> git bisect bad efb520aa333b2f11daaaaa13f4a598b5ae4ae823
>>>> # bad: [2258bdebb55e3ad3d30fd3849ddb955ff36825de] mm/zsmalloc: don't
>>>> hold locks of all pages when free_zspage()
>>>> git bisect bad 2258bdebb55e3ad3d30fd3849ddb955ff36825de
>>>> # bad: [7fc0be45acf2878cbacc4dba56923c34c3fd8b1e] mm: remove
>>>> total_mapcount()
>>>> git bisect bad 7fc0be45acf2878cbacc4dba56923c34c3fd8b1e
>>>> # good: [d55fac55da2f87ad5a99178e107df09770bbc411] mm: thp: split huge
>>>> page to any lower order pages
>>>> git bisect good d55fac55da2f87ad5a99178e107df09770bbc411
>>>> # bad: [4050d591c1aaf9336c08511fa5984827186e9ad1] mm/memfd: refactor
>>>> memfd_tag_pins() and memfd_wait_for_pins()
>>>> git bisect bad 4050d591c1aaf9336c08511fa5984827186e9ad1
>>>> # bad: [c0ba89c29ef559c95273feb481b049f622c43c17] mm: huge_memory:
>>>> enable debugfs to split huge pages to any order
>>>> git bisect bad c0ba89c29ef559c95273feb481b049f622c43c17
>>>> # first bad commit: [c0ba89c29ef559c95273feb481b049f622c43c17] mm:
>>>> huge_memory: enable debugfs to split huge pages to any order
>>>>
>>>>
>>>> Thanks,
>>>> Aishwarya
>>
>>
>> --
>> Best Regards,
>> Yan, Zi


--
Best Regards,
Yan, Zi

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