On Thu, Feb 4, 2021 at 11:54 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
>
> When we free a HugeTLB page to the buddy allocator, we should allocate the
> vmemmap pages associated with it. But we may cannot allocate vmemmap pages
> when the system is under memory pressure, in this case, we just refuse to
> free the HugeTLB page instead of looping forever trying to allocate the
> pages.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> include/linux/mm.h | 2 ++
> mm/hugetlb.c | 19 ++++++++++++-
> mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
> mm/hugetlb_vmemmap.h | 8 ++++++
> mm/sparse-vmemmap.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 132 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index d7dddf334779..33c5911afe18 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2981,6 +2981,8 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
>
> void vmemmap_remap_free(unsigned long start, unsigned long end,
> unsigned long reuse);
> +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> + unsigned long reuse, gfp_t gfp_mask);
>
> void *sparse_buffer_alloc(unsigned long size);
> struct page * __populate_section_memmap(unsigned long pfn,
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4cfca27c6d32..5518283aa667 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)
> h->resv_huge_pages++;
>
> if (HPageTemporary(page)) {
> - list_del(&page->lru);
> ClearHPageTemporary(page);
> +
> + if (alloc_huge_page_vmemmap(h, page, GFP_ATOMIC)) {
> + h->surplus_huge_pages++;
> + h->surplus_huge_pages_node[nid]++;
> + goto enqueue;
> + }
> + list_del(&page->lru);
> update_and_free_page(h, page);
> } else if (h->surplus_huge_pages_node[nid]) {
> + if (alloc_huge_page_vmemmap(h, page, GFP_ATOMIC))
> + goto enqueue;
> +
> /* remove the page from active list */
> list_del(&page->lru);
> update_and_free_page(h, page);
> h->surplus_huge_pages--;
> h->surplus_huge_pages_node[nid]--;
> } else {
> +enqueue:
> arch_clear_hugepage_flags(page);
> enqueue_huge_page(h, page);
> }
> @@ -1693,6 +1703,10 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> struct page *page =
> list_entry(h->hugepage_freelists[node].next,
> struct page, lru);
> +
> + if (alloc_huge_page_vmemmap(h, page, GFP_ATOMIC))
> + break;
> +
> list_del(&page->lru);
> h->free_huge_pages--;
> h->free_huge_pages_node[node]--;
> @@ -1760,6 +1774,9 @@ int dissolve_free_huge_page(struct page *page)
> goto retry;
> }
>
> + if (alloc_huge_page_vmemmap(h, head, GFP_ATOMIC))
> + goto out;
> +
Hi Oscar,
Because we allocate vmemmap pages and do the remapping
before setting the PG_hwpoision of tail struct page. So we do
not need the following patch.
[1] https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-7-songmuchun@xxxxxxxxxxxxx/
> /*
> * Move PageHWPoison flag from head page to the raw error page,
> * which makes any subpages rather than the error page reusable.
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index ddd872ab6180..0bd6b8d7282d 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -169,6 +169,8 @@
> * (last) level. So this type of HugeTLB page can be optimized only when its
> * size of the struct page structs is greater than 2 pages.
> */
> +#define pr_fmt(fmt) "HugeTLB: " fmt
> +
> #include "hugetlb_vmemmap.h"
>
> /*
> @@ -198,6 +200,34 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
> return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> }
>
> +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head, gfp_t gfp_mask)
> +{
> + int ret;
> + unsigned long vmemmap_addr = (unsigned long)head;
> + unsigned long vmemmap_end, vmemmap_reuse;
> +
> + if (!free_vmemmap_pages_per_hpage(h))
> + return 0;
> +
> + vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> + vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
> + vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
> +
> + /*
> + * The pages which the vmemmap virtual address range [@vmemmap_addr,
> + * @vmemmap_end) are mapped to are freed to the buddy allocator, and
> + * the range is mapped to the page which @vmemmap_reuse is mapped to.
> + * When a HugeTLB page is freed to the buddy allocator, previously
> + * discarded vmemmap pages must be allocated and remapping.
> + */
> + ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
> + gfp_mask | __GFP_NOWARN | __GFP_THISNODE);
> + if (ret == -ENOMEM)
> + pr_info("cannot alloc vmemmap pages\n");
> +
> + return ret;
> +}
> +
> void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> {
> unsigned long vmemmap_addr = (unsigned long)head;
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 6923f03534d5..6f89a9eed02c 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -11,8 +11,16 @@
> #include <linux/hugetlb.h>
>
> #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head,
> + gfp_t gfp_mask);
> void free_huge_page_vmemmap(struct hstate *h, struct page *head);
> #else
> +static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head,
> + gfp_t gfp_mask)
> +{
> + return 0;
> +}
> +
> static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> {
> }
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 50c1dc00b686..277eb43aebd5 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -40,7 +40,8 @@
> * @remap_pte: called for each non-empty PTE (lowest-level) entry.
> * @reuse_page: the page which is reused for the tail vmemmap pages.
> * @reuse_addr: the virtual address of the @reuse_page page.
> - * @vmemmap_pages: the list head of the vmemmap pages that can be freed.
> + * @vmemmap_pages: the list head of the vmemmap pages that can be freed
> + * or is mapped from.
> */
> struct vmemmap_remap_walk {
> void (*remap_pte)(pte_t *pte, unsigned long addr,
> @@ -237,6 +238,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,
> free_vmemmap_page_list(&vmemmap_pages);
> }
>
> +static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
> + struct vmemmap_remap_walk *walk)
> +{
> + pgprot_t pgprot = PAGE_KERNEL;
> + struct page *page;
> + void *to;
> +
> + BUG_ON(pte_page(*pte) != walk->reuse_page);
> +
> + page = list_first_entry(walk->vmemmap_pages, struct page, lru);
> + list_del(&page->lru);
> + to = page_to_virt(page);
> + copy_page(to, (void *)walk->reuse_addr);
> +
> + set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
> +}
> +
> +static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> + gfp_t gfp_mask, struct list_head *list)
> +{
> + unsigned long addr;
> + int nid = page_to_nid((const void *)start);
> + struct page *page, *next;
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE) {
> + page = alloc_pages_node(nid, gfp_mask, 0);
> + if (!page)
> + goto out;
> + list_add_tail(&page->lru, list);
> + }
> +
> + return 0;
> +out:
> + list_for_each_entry_safe(page, next, list, lru)
> + __free_pages(page, 0);
> + return -ENOMEM;
> +}
> +
> +/**
> + * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
> + * to the page which is from the @vmemmap_pages
> + * respectively.
> + * @start: start address of the vmemmap virtual address range that we want
> + * to remap.
> + * @end: end address of the vmemmap virtual address range that we want to
> + * remap.
> + * @reuse: reuse address.
> + * @gpf_mask: GFP flag for allocating vmemmap pages.
> + */
> +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> + unsigned long reuse, gfp_t gfp_mask)
> +{
> + LIST_HEAD(vmemmap_pages);
> + struct vmemmap_remap_walk walk = {
> + .remap_pte = vmemmap_restore_pte,
> + .reuse_addr = reuse,
> + .vmemmap_pages = &vmemmap_pages,
> + };
> +
> + /* See the comment in the vmemmap_remap_free(). */
> + BUG_ON(start - reuse != PAGE_SIZE);
> +
> + might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> +
> + if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
> + return -ENOMEM;
> +
> + vmemmap_remap_range(reuse, end, &walk);
> +
> + return 0;
> +}
> +
> /*
> * Allocate a block of memory to be used to back the virtual memory map
> * or to back the page tables that are used to create the mapping.
> --
> 2.11.0
>
