Re: [PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio

[David Hildenbrand (Arm)]

On 7/22/26 10:27, Vlastimil Babka (SUSE) wrote:
> On 7/17/26 15:06, William Roche wrote:
>> On 7/17/26 12:18, David Hildenbrand (Arm) wrote:
>>>
>>> I still don't like the complexity of this, in particular, as we have different
>>> mechanisms in the page allocator already to try handling this,
>>>
>>> We also do have cases where we set the hwpoison bit, while a page is just about
>>> to get allocated from the buddy. So before we take it off the buddy, we might
>>> just hand out the page.
>>>
>>> check_new_pages() seems to check for PageHWPoison() and make us not hand out
>>> such pages. It's guarded by "check_pages" but it seems to do exactly what we are
>>> looking for, now?
>>
>>
>> Just adding a comment about this aspect:
>> The check_new_pages() mechanism used by the __rmqueue functions should
>> filter these pages out, but this has been disabled by default in 2023
>> with:
>> [PATCH] mm, page_alloc: reduce page alloc/free sanity checks
>> https://lore.kernel.org/all/20230216095131.17336-1-vbabka@xxxxxxx
>>
>> So it would need to be enabled back, taking some of the performance hit.
>> (and I personally think that it has to be done)
> 
> Would it truly fix the issue, or rather there would still be a race window
> left where we check that there's no hwpoison flag in the re-enabled check,
> and only then someone sets it?

Why are we checking PageHWPoison at all then in check_new_page()?

I think we created a mess.

The PageHWPoison check is not just a "nice to have" sanity check for kernel bugs.

So it should never have been optimized out that way before reworking the bigger
picture.

> 
> Also, can the hardware actually detect a problem with a page that nobody
> accesses? I guess if yes, it's only in some corner cases.

Yes, quite frequently I think.

> 
> So I'm wary about penalizing the allocator paths again.

I get the feeling that we don't have a proper plan on how to handle HWPoisoned
pages. We should take a step back and discuss how we actually want to handle
them instead of optimizing here and there and creating more of a mess.

-- 
Cheers,

David