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SubjectRe: [PATCH v2 1/2] mm: Make alloc_contig_range handle free hugetlb pages
On 2021-02-19 03:10, Mike Kravetz wrote:
> Those counts will be wrong as there are no huge pages on the node.
>
> I'll think about this more tomorrow.
> Pretty sure this is an issue, but I could be wrong. Just wanted to
> give
> a heads up.

Yes, this is a problem, although the fixup would be to check whether we
have any hugepages.

Nevertheless, I think we should not be touching surplus at all but
rather make the page temporary.
I am exploring making migrate_pages() handle free hugepages as Michal
suggested, so the approach is cleaner and we do not need extra
functions. I yet have to see if that is feasible, as some issues come to
my mind like the page needs to be in a list to go to migrate_pages, but
if it is in that list, it is not in hugepages_freelist, and that could
disrupt userspace as it could not dequeue hugepages if it demands it.
I have to check. Shoult not be possible, we can always make the page
temporary here.

> --
> Mike Kravetz
>
>> + }
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +bool isolate_or_dissolve_huge_page(struct page *page)
>> +{
>> + struct hstate *h = NULL;
>> + struct page *head;
>> + bool ret = false;
>> +
>> + spin_lock(&hugetlb_lock);
>> + if (PageHuge(page)) {
>> + head = compound_head(page);
>> + h = page_hstate(head);
>> + }
>> + spin_unlock(&hugetlb_lock);
>> +
>> + /*
>> + * The page might have been dissolved from under our feet.
>> + * If that is the case, return success as if we dissolved it
>> ourselves.
>> + */
>> + if (!h)
>> + return true;
>> +
>> + /*
>> + * Fence off gigantic pages as there is a cyclic dependency
>> + * between alloc_contig_range and them.
>> + */
>> + if (hstate_is_gigantic(h))
>> + return ret;
>> +
>> + if(!page_count(head) && alloc_and_dissolve_huge_page(h, head))
>> + ret = true;
>> +
>> + return ret;
>> +}
>> +
>> struct page *alloc_huge_page(struct vm_area_struct *vma,
>> unsigned long addr, int avoid_reserve)
>> {
>>

--
Oscar Salvador
SUSE L3

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