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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a14b69b9-b6f2-4271-7103-08de08113a00 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Oct 2025 15:25:21.5363 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: wAEyzDxnxGDSKpOiLAMUPcVqEA0D64QcjFoqXzl7lTt8+YyRLfxdF2+h8ht04NKy X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB9490 On 9 Oct 2025, at 3:39, Miaohe Lin wrote: > On 2025/10/3 1:47, jane.chu@oracle.com wrote: >> >> >> On 10/2/2025 6:54 AM, Zi Yan wrote: >>> On 2 Oct 2025, at 1:23, jane.chu@oracle.com wrote: >>> >>>> On 10/1/2025 7:04 PM, Zi Yan wrote: >>>>> On 1 Oct 2025, at 20:38, Zi Yan wrote: >>>>> >>>>>> On 1 Oct 2025, at 19:58, jane.chu@oracle.com wrote: >>>>>> >>>>>>> Hi, Zi Yan, >>>>>>> >>>>>>> On 9/30/2025 9:51 PM, syzbot wrote: >>>>>>>> Hello, >>>>>>>> >>>>>>>> syzbot has tested the proposed patch but the reproducer is still t= riggering an issue: >>>>>>>> lost connection to test machine >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> Tested on: >>>>>>>> >>>>>>>> commit:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 d8795075 m= m/huge_memory: do not change split_huge_page.. >>>>>>>> git tree:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 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=3D17ce96= e2580000 >>>>>>>> kernel config:=C2=A0 https://syzkaller.appspot.com/x/.config?x=3D7= 14d45b6135c308e >>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=3De6367ea2= fdab6ed46056 >>>>>>>> compiler:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Debian clang version= 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian L= LD 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.=C2=A0 Perhaps on ARM64, the page cache pages o= f /dev/nullb0 in >>>>>> Yes, it only has the first patch, which fails a split if it cannot b= e >>>>>> 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: >>>>>>> [=C2=A0 200.378989][T18221] Memory failure: 0x124d30: recovery acti= on 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 ea= rlier - >>>>>>> https://lore.kernel.org/lkml/7577871f-06be-492d-b6d7-8404d7a045e0@o= racle.com/ >>>>>>> >>>>>>> So that in the madvise HWPOISON cases, large huge pages are splitte= d 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 a= nd make >>>>>> syzbot check it again. >>>>> >>>>> >>>>> #syz test: https://github.com/x-y-z/linux-dev.git fix_split_page_min_= order_and_opt_memory_failure-for-kernelci >>>>> >>>> >>>> There is a bug here, >>>> >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (try_to_split_thp_page(p= , new_order, false) || new_order) { >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 res= =3D -EHWPOISON; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kil= l_procs_now(p, pfn, flags, folio);=C2=A0 <--- >>>> >>>> If try_to_split_thp_page() succeeded on min_order, 'folio' should be r= etaken:=C2=A0 folio =3D page_folio(page) before moving on to kill_procs_now= (). >>> >>> Thank you for pointing it out. Let me fix it and let syzbot test it aga= in. >>> > > Sorry for late. I just got back from my vacation. :) > >>> BTW, do you mind explaining why soft offline case does not want to spli= t? >>> Like memory failure case, splitting it would make other after-split fol= ios >>> available. >> >> That's exactly what I think.=C2=A0 Let's wait for Miaohe, not sure if he= has other concern. > > It might be because even if split is skipped, the folio is still accessib= le (thus available) > from user sapce and premature split might lead to potential performance l= oss. But it's fine > to me to split folio first in soft offline case. No strong opinion. Thanks for the explanation. I will add a comment about this. We can always = do the split at soft offline when we find it useful. I will send the patches out. -- Best Regards, Yan, Zi