On 2024/7/17 5:33, Jane Chu wrote:
> Hi, Matthew,
>
> On 7/16/2024 8:12 AM, Matthew Wilcox wrote:
>> I was going to send this patch:
>>
>> +++ b/mm/madvise.c
>> @@ -1136,9 +1136,10 @@ static int madvise_inject_error(int behavior,
>> /*
>> * When soft offlining hugepages, after migrating the page
>> * we dissolve it, therefore in the second loop "page" will
>> - * no longer be a compound page.
>> + * no longer be part of a large folio.
>> */
>> - size = page_size(compound_head(page));
>> + size = folio_size(page_folio(page));
>> + start = start & ~(size - 1);
>>
>> if (behavior == MADV_SOFT_OFFLINE) {
>> pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
>>
>> because right now if you start in the middle of (e.g.) an order-4 folio
>> followed by an order-0 folio, you'll skip the order-0 folio immediately
>> following it.
>>
>> But then I realised that we can come to this path in the middle of
>> a large file-backed folio that's mapped misaligned and has a COW page
>> in the middle, and the whole thing is just misguided. So I gave up.
>> Anyone want to take a crack at fixing & testing this?
>
> Thanks for the report.
Thanks both for your thoughts.
>
> My understanding is, we should run folio_test_large() upfront, and treat both ends as special case
>
> unless they're folio_size aligned, and iterate in folio_size for the middle. I think this should work for
>
> hugetlb and large folio in general, but I need to confirm this with tests.
>
> Any thoughts?
I might be wrong but there might be some corner cases even if they're folio_size aligned.
For example, if pte[0] points to a pte mapped thp and pte[1..n] are cowed pages, these cowed
pages might be skipped in next loop because folio_size covers them but they doesn't belong to
this thp? Will it be better to decide @size upon pte entry?
Thanks.
.
