On Sun, Jan 17, 2021 at 11:10:46PM +0800, Muchun Song wrote:
> When we free a HugeTLB page to the buddy allocator, we should allocate the
> vmemmap pages associated with it. We can do that in the __free_hugepage()
> before freeing it to buddy.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
This series has grown a certain grade of madurity and improvment, but it seems
to me that we have been stuck in this patch (and patch#4) for quite some time.
Would it be acceptable for a first implementation to not let hugetlb pages to
be freed when this feature is in use?
This would simplify things for now, as we could get rid of patch#4 and patch#5.
We can always extend functionality once this has been merged, right?
Of course, this means that e.g: memory-hotplug (hot-remove) will not fully work
when this in place, but well.
I would like to hear what others think, but in my opinion it would be a big step
to move on.
> ---
> include/linux/mm.h | 2 ++
> mm/hugetlb.c | 2 ++
> mm/hugetlb_vmemmap.c | 15 ++++++++++
> mm/hugetlb_vmemmap.h | 5 ++++
> mm/sparse-vmemmap.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 100 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f928994ed273..16b55d13b0ab 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3007,6 +3007,8 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
>
> void vmemmap_remap_free(unsigned long start, unsigned long end,
> unsigned long reuse);
> +void vmemmap_remap_alloc(unsigned long start, unsigned long end,
> + unsigned long reuse);
>
> 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 c165186ec2cf..d11c32fcdb38 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1326,6 +1326,8 @@ static void update_hpage_vmemmap_workfn(struct work_struct *work)
> page->mapping = NULL;
> h = page_hstate(page);
>
> + alloc_huge_page_vmemmap(h, page);
> +
> spin_lock(&hugetlb_lock);
> __free_hugepage(h, page);
> spin_unlock(&hugetlb_lock);
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 19f1898aaede..6108ae80314f 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -183,6 +183,21 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
> return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> }
>
> +void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> + unsigned long vmemmap_addr = (unsigned long)head;
> + unsigned long vmemmap_end, vmemmap_reuse;
> +
> + if (!free_vmemmap_pages_per_hpage(h))
> + return;
> +
> + vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> + vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
> + vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
> +
> + vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse);
> +}
> +
> 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 01f8637adbe0..b2c8d2f11d48 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -11,6 +11,7 @@
> #include <linux/hugetlb.h>
>
> #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +void alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
> void free_huge_page_vmemmap(struct hstate *h, struct page *head);
>
> /*
> @@ -25,6 +26,10 @@ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> return 0;
> }
> #else
> +static inline void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> +}
> +
> 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 ce4be1fa93c2..3b146d5949f3 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -29,6 +29,7 @@
> #include <linux/sched.h>
> #include <linux/pgtable.h>
> #include <linux/bootmem_info.h>
> +#include <linux/delay.h>
>
> #include <asm/dma.h>
> #include <asm/pgalloc.h>
> @@ -40,7 +41,8 @@
> * @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,
> @@ -50,6 +52,10 @@ struct vmemmap_remap_walk {
> struct list_head *vmemmap_pages;
> };
>
> +/* The gfp mask of allocating vmemmap page */
> +#define GFP_VMEMMAP_PAGE \
> + (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN | __GFP_THISNODE)
> +
> static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
> unsigned long end,
> struct vmemmap_remap_walk *walk)
> @@ -228,6 +234,75 @@ 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 void alloc_vmemmap_page_list(struct list_head *list,
> + unsigned long start, unsigned long end)
> +{
> + unsigned long addr;
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE) {
> + struct page *page;
> + int nid = page_to_nid((const void *)addr);
> +
> +retry:
> + page = alloc_pages_node(nid, GFP_VMEMMAP_PAGE, 0);
> + if (unlikely(!page)) {
> + msleep(100);
> + /*
> + * We should retry infinitely, because we cannot
> + * handle allocation failures. Once we allocate
> + * vmemmap pages successfully, then we can free
> + * a HugeTLB page.
> + */
> + goto retry;
> + }
> + list_add_tail(&page->lru, list);
> + }
> +}
> +
> +/**
> + * 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.
> + * @end: end address of the vmemmap virtual address range.
> + * @reuse: reuse address.
> + */
> +void vmemmap_remap_alloc(unsigned long start, unsigned long end,
> + unsigned long reuse)
> +{
> + LIST_HEAD(vmemmap_pages);
> + struct vmemmap_remap_walk walk = {
> + .remap_pte = vmemmap_restore_pte,
> + .reuse_addr = reuse,
> + .vmemmap_pages = &vmemmap_pages,
> + };
> +
> + might_sleep();
> +
> + /* See the comment in the vmemmap_remap_free(). */
> + BUG_ON(start - reuse != PAGE_SIZE);
> +
> + alloc_vmemmap_page_list(&vmemmap_pages, start, end);
> + vmemmap_remap_range(reuse, end, &walk);
> +}
> +
> /*
> * 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
>
>
--
Oscar Salvador
SUSE L3
