Re: [syzbot] [mm?] WARNING in memory_failure

jane.chu
2025-10-01T23:58:58Z

Hi, Zi Yan,

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

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 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.

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/

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.

thanks,
-jane