On 1 Oct 2025, at 19:58, jane.chu@oracle.com wrote:

Hi, Zi Yan,

On 9/30/2025 9:51 PM, syzbot wrote:

quoted

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
lost connection to test machine



Tested on:

commit:         d8795075 mm/huge_memory: do not change split_huge_page..
git tree:       https://github.com/x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=17ce96e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=714d45b6135c308e
dashboard link: https://syzkaller.appspot.com/bug?extid=e6367ea2fdab6ed46056
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

Note: no patches were applied.

Thank you for looking into this.

My hunch is that
  https://github.com/x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci
alone is not enough.  Perhaps on ARM64, the page cache pages of /dev/nullb0 in

Yes, it only has the first patch, which fails a split if it cannot be
split to the intended order (order-0 in this case).

the test case are probably with min_order > 0, therefore THP split fails, as the console message show:
[  200.378989][T18221] Memory failure: 0x124d30: recovery action for unsplit thp: Failed

With lots of poisoned THP pages stuck in the page cache, OOM could trigger too soon.

That is my understanding too. Thanks for the confirmation.

I think it's worth to try add the additional changes I suggested earlier -
https://lore.kernel.org/lkml/7577871f-06be-492d-b6d7-8404d7a045e0@oracle.com/ (local)

So that in the madvise HWPOISON cases, large huge pages are splitted to smaller huge pages, and most of them remain usable in the page cache.

Yep, I am going to incorporate your suggestion as the second patch and make
syzbot check it again.

Best Regards,
Yan, Zi