On 10/6/21 1:41 AM, Oscar Salvador wrote:
> On Fri, Oct 01, 2021 at 10:52:10AM -0700, Mike Kravetz wrote:
>> Demote page functionality will split a huge page into a number of huge
>> pages of a smaller size. For example, on x86 a 1GB huge page can be
>> demoted into 512 2M huge pages. Demotion is done 'in place' by simply
>> splitting the huge page.
>>
>> Added '*_for_demote' wrappers for remove_hugetlb_page,
>> destroy_compound_gigantic_page and prep_compound_gigantic_page for use
>> by demote code.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> ---
>> mm/hugetlb.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 74 insertions(+), 8 deletions(-)
>>
> ...
>> +static int demote_free_huge_page(struct hstate *h, struct page *page)
>> +{
>> + int i, nid = page_to_nid(page);
>> + struct hstate *target_hstate;
>> + int rc = 0;
>> +
>> + target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
>> +
>> + remove_hugetlb_page_for_demote(h, page, false);
>> + spin_unlock_irq(&hugetlb_lock);
>> +
>> + rc = alloc_huge_page_vmemmap(h, page);
>> + if (rc) {
>> + /* Allocation of vmemmmap failed, we can not demote page */
>> + spin_lock_irq(&hugetlb_lock);
>> + set_page_refcounted(page);
>> + add_hugetlb_page(h, page, false);
>> + return rc;
>> + }
>
> Question: You keep the original error code returned from alloc_huge_page_vmemmap()
> here, but then you lose it on demote_pool_huge_page() when doing the
> !demote_free_huge_page. Would not make more sense to keep it all the way down to
> demote_store() in case you want to return the actual error code?
>
Yes, I will return it all the way to demote_store (and the user).
>> +
>> + /*
>> + * Use destroy_compound_gigantic_page_for_demote for all huge page
>> + * sizes as it will not ref count pages.
>> + */
>> + destroy_compound_gigantic_page_for_demote(page, huge_page_order(h));
>
> It seems that for now we only allow gigantic pages to be demoted, but
> destroy_compound_gigantic_page_for_demote feels kind of wrong, even
> if it is only a wrapper that ends up calling _*gigantic_ functions.
>
> We want a routine that destroy a hugetlb to be demoted into smaller hugetlb
> pages, so the name gigantic makes little sense to appear in my opinion.
>
Agree, I do not love the name. Since it is only a wrapper, how about
destroy_hugetlb_page_for_demote? And, change those other *_for_demote
wrappers to similiarly not have gigantic in their names.
>> static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>> __must_hold(&hugetlb_lock)
>> {
>> + int nr_nodes, node;
>> + struct page *page;
>> int rc = 0;
>>
>> lockdep_assert_held(&hugetlb_lock);
>> @@ -3313,9 +3377,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>> if (!h->demote_order)
>> return rc;
>>
>> - /*
>> - * TODO - demote fucntionality will be added in subsequent patch
>> - */
>> + for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
>> + if (!list_empty(&h->hugepage_freelists[node])) {
>> + page = list_entry(h->hugepage_freelists[node].next,
>> + struct page, lru);
>> + rc = !demote_free_huge_page(h, page);
>
> I kinda dislike this as I pointed out.
>
Will change.
Thanks for all your comments!
--
Mike Kravetz
