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

Ryan Roberts
2024-03-01T14:18:26Z

On 01/03/2024 13:53, Zi Yan wrote:
> 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.

Thanks - appeciated!

Although I agree it might be a tall order create and mount an XFS fs in
run_vmtests.sh. Perhaps it might be good enough to add an optional param to the
test to pass a path when running the test manually, and if that's not provided,
just try to create a temp file in the current dir and skip if its not the right
sort of fs?

>
>>
>>> 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