Re: [PATCH v8 2/6] mm/memory-failure: surface unhandlable kernel pages as -ENOTRECOVERABLE

[Miaohe Lin]

On 2026/6/2 17:41, David Hildenbrand (Arm) wrote:
> On 6/2/26 05:08, Miaohe Lin wrote:
>> On 2026/6/1 21:22, David Hildenbrand (Arm) wrote:
>>> On 6/1/26 14:28, Miaohe Lin wrote:
>>>>
>>>> Thanks for your patch.
>>>>
>>>>
>>>> Once shake_page finds a lightweight range-based way to shrink slab, slab pages could be freed
>>>> into buddy and above PageSlab test should be removed then. Maybe add a TODO or XXX here?
>>>>
>>>>
>>>> I'm not sure but is it safe or a common way to test PageReserved, PageSlab,
>>>> PageTable and PageLargeKmalloc without extra page refcnt?
>>>
>>> Checking typed pages in a racy fashion is fine (PageSlab, PageTable,
>>> PageLargeKmalloc).
>>
>> Got it. Thanks.
>>
>>> Checking PageReserved in a racy fashion is fine as well. TESTPAGEFLAG() will
>>> allow checking it on compound pages.
>>
>> It seems PageReserved is not intended to be set on compound pages. I see there are PF_NO_COMPOUND
>> in its definition: PAGEFLAG(Reserved, reserved, PF_NO_COMPOUND).
>>
>>>
>>> For PageLargeKmalloc, we would want to check the head page, though. The page
>>> type is only stored for the head page.
>>
>> Maybe we should check the head page for PageSlab and PageTable too? alloc_slab_page only
>> set PageSlab on the head page and __pagetable_ctor uses __folio_set_pgtable to set PageTable
>> on folio.
>>
>>>
>>> So maybe we want to lookup the compound head (if any) and perform the type
>>> checks against that?
>>
>> Maybe we should or we might miss some pages that could have been handled. And
>> if compound head is required, should we hold an extra page refcnt to guard against
>> possible folio split race?
> 
> Races are fine. We might miss some pages, but that can happen on races either way.
> 
> 
> I'd just do something like
> 
> if (PageReserved(page))
> 	return true;
> 
> head = compound_head(page);

If @head is split just after compound_head. And then @head is freed into buddy and re-allocated as slab
page while @page is still in the buddy. We would panic on this scene as @head is PageSlab. But we were
supposed to successfully handle @page. Or am I miss something?

Thanks.
.

> return PageSlab(head) || ...;
> 	
>