On 2022/3/27 4:14, Rik van Riel wrote:
> On Sat, 2022-03-26 at 15:48 +0800, Miaohe Lin wrote:
>> On 2022/3/26 4:14, Rik van Riel wrote:
>>>
>>> +++ b/mm/memory.c
>>> @@ -3918,14 +3918,18 @@ static vm_fault_t __do_fault(struct
>>> vm_fault *vmf)
>>> return ret;
>>>
>>> if (unlikely(PageHWPoison(vmf->page))) {
>>> + struct page *page = vmf->page;
>>> vm_fault_t poisonret = VM_FAULT_HWPOISON;
>>> if (ret & VM_FAULT_LOCKED) {
>>> + if (page_mapped(page))
>>> + unmap_mapping_pages(page_mapping(pa
>>> ge),
>>> + page->index, 1,
>>> false);
>>
>> It seems this unmap_mapping_pages also helps the success rate of the
>> below invalidate_inode_page.
>>
>
> That is indeed what it is supposed to do.
>
> It isn't fool proof, since you can still end up
> with dirty pages that don't get cleaned immediately,
> but it seems to turn infinite loops of a program
> being killed every time it's started into a more
> manageable situation where the task succeeds again
> pretty quickly.
Looks convincing to me.
>
>>> /* Retry if a clean page was removed from
>>> the cache. */
>>> - if (invalidate_inode_page(vmf->page))
>>> - poisonret = 0;
>>> - unlock_page(vmf->page);
>>> + if (invalidate_inode_page(page))
>>> + poisonret = VM_FAULT_NOPAGE;
>>> + unlock_page(page);
>>> }
>>> - put_page(vmf->page);
>>> + put_page(page);
>>
>> Do we use page instead of vmf->page just for simplicity? Or there is
>> some other concern?
>>
>
> Just a simplification, and not dereferencing the same thing
> 6 times.
>
I see. :)
>>> vmf->page = NULL;
>>
>> We return either VM_FAULT_NOPAGE or VM_FAULT_HWPOISON with vmf->page
>> = NULL. If any case,
>> finish_fault won't be called later. So I think your fix is right.
>
> Want to send in a Reviewed-by or Acked-by? :)
>
Sure, but when I think more about this, it seems this fix isn't ideal:
If VM_FAULT_NOPAGE is returned with page table unset, the process will
re-trigger page fault again and again until invalidate_inode_page succeeds
to evict the inode page. This might hang the process a really long time.
Or am I miss something?
Thanks.
