On Fri, Oct 08, 2021 at 01:57:48PM -0700, Mike Kravetz wrote:
> From 25e4dac59f4d203f3a7e86d3591d70c1e956d11c Mon Sep 17 00:00:00 2001
> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Date: Fri, 8 Oct 2021 13:21:21 -0700
> Subject: [PATCH v4 5/5] hugetlb: add hugetlb demote page support
>
> 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_hugetlb_page and prep_compound_gigantic_page for use
> by demote code.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> mm/hugetlb.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 92 insertions(+), 8 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 794e0c4c1b3c..e1883510309a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1270,7 +1270,7 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
> ((node = hstate_next_node_to_free(hs, mask)) || 1); \
> nr_nodes--)
>
> -#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
> +/* used to demote non-gigantic_huge pages as well */
> static void __destroy_compound_gigantic_page(struct page *page,
> unsigned int order, bool demote)
> {
> @@ -1293,6 +1293,13 @@ static void __destroy_compound_gigantic_page(struct page *page,
> __ClearPageHead(page);
> }
>
> +static void destroy_compound_hugetlb_page_for_demote(struct page *page,
> + unsigned int order)
> +{
> + __destroy_compound_gigantic_page(page, order, true);
> +}
> +
> +#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
> static void destroy_compound_gigantic_page(struct page *page,
> unsigned int order)
> {
> @@ -1438,6 +1445,12 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
> __remove_hugetlb_page(h, page, adjust_surplus, false);
> }
>
> +static void remove_hugetlb_page_for_demote(struct hstate *h, struct page *page,
> + bool adjust_surplus)
> +{
> + __remove_hugetlb_page(h, page, adjust_surplus, true);
> +}
> +
> static void add_hugetlb_page(struct hstate *h, struct page *page,
> bool adjust_surplus)
> {
> @@ -1779,6 +1792,12 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
> return __prep_compound_gigantic_page(page, order, false);
> }
>
> +static bool prep_compound_gigantic_page_for_demote(struct page *page,
> + unsigned int order)
> +{
> + return __prep_compound_gigantic_page(page, order, true);
> +}
> +
> /*
> * PageHuge() only returns true for hugetlbfs pages, but not for normal or
> * transparent huge pages. See the PageTransHuge() documentation for more
> @@ -3304,9 +3323,72 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> return 0;
> }
>
> +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;
> + }
> +
> + /*
> + * Use destroy_compound_hugetlb_page_for_demote for all huge page
> + * sizes as it will not ref count pages.
> + */
> + destroy_compound_hugetlb_page_for_demote(page, huge_page_order(h));
> +
> + /*
> + * Taking target hstate mutex synchronizes with set_max_huge_pages.
> + * Without the mutex, pages added to target hstate could be marked
> + * as surplus.
> + *
> + * Note that we already hold h->resize_lock. To prevent deadlock,
> + * use the convention of always taking larger size hstate mutex first.
> + */
> + mutex_lock(&target_hstate->resize_lock);
> + for (i = 0; i < pages_per_huge_page(h);
> + i += pages_per_huge_page(target_hstate)) {
> + if (hstate_is_gigantic(target_hstate))
> + prep_compound_gigantic_page_for_demote(page + i,
> + target_hstate->order);
> + else
> + prep_compound_page(page + i, target_hstate->order);
> + set_page_private(page + i, 0);
> + set_page_refcounted(page + i);
> + prep_new_huge_page(target_hstate, page + i, nid);
> + put_page(page + i);
> + }
> + mutex_unlock(&target_hstate->resize_lock);
> +
> + spin_lock_irq(&hugetlb_lock);
> +
> + /*
> + * Not absolutely necessary, but for consistency update max_huge_pages
> + * based on pool changes for the demoted page.
> + */
> + h->max_huge_pages--;
> + target_hstate->max_huge_pages += pages_per_huge_page(h);
> +
> + return rc;
> +}
> +
> 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);
> @@ -3317,9 +3399,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> return -EINVAL; /* internal error */
> }
>
> - /*
> - * 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);
> + break;
> + }
> + }
> +
> return rc;
> }
>
> @@ -3554,10 +3642,6 @@ static ssize_t demote_store(struct kobject *kobj,
> /*
> * Check for available pages to demote each time thorough the
> * loop as demote_pool_huge_page will drop hugetlb_lock.
> - *
> - * NOTE: demote_pool_huge_page does not yet drop hugetlb_lock
> - * but will when full demote functionality is added in a later
> - * patch.
> */
> if (nid != NUMA_NO_NODE)
> nr_available = h->free_huge_pages_node[nid];
> --
> 2.31.1
>
>
--
Oscar Salvador
SUSE Labs
