Re: [PATCH 1/1] hugetlbfs: handle pages higher order than MAX_ORDER

Mel Gorman
2008-10-08T14:57:00Z

On (08/10/08 10:33), Andy Whitcroft didst pronounce:
> When working with hugepages, hugetlbfs assumes that those hugepages
> are smaller than MAX_ORDER. Specifically it assumes that the mem_map
> is contigious and uses that to optimise access to the elements of the
> mem_map that represent the hugepage. Gigantic pages (such as 16GB pages
> on powerpc) by definition are of greater order than MAX_ORDER (larger
> than MAX_ORDER_NR_PAGES in size). This means that we can no longer make
> use of the buddy alloctor guarentees for the contiguity of the mem_map,
> which ensures that the mem_map is at least contigious for maximmally
> aligned areas of MAX_ORDER_NR_PAGES pages.
>
> This patch adds new mem_map accessors and iterator helpers which handle
> any discontiguity at MAX_ORDER_NR_PAGES boundaries. It then uses these
> within copy_huge_page, clear_huge_page, and follow_hugetlb_page to allow
> these to handle gigantic pages.
>
> Signed-off-by: Andy Whitcroft <apw@shadowen.org>

Acked-by: Mel Gorman <mel@csn.ul.ie>

> ---
> mm/hugetlb.c | 15 ++++++++++-----
> mm/internal.h | 28 ++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+), 5 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 67a7119..bb5cf81 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -357,11 +357,12 @@ static void clear_huge_page(struct page *page,
> unsigned long addr, unsigned long sz)
> {
> int i;
> + struct page *p = page;
>
> might_sleep();
> - for (i = 0; i < sz/PAGE_SIZE; i++) {
> + for (i = 0; i < sz/PAGE_SIZE; i++, p = mem_map_next(p, page, i)) {
> cond_resched();
> - clear_user_highpage(page + i, addr + i * PAGE_SIZE);
> + clear_user_highpage(p, addr + i * PAGE_SIZE);
> }
> }
>
> @@ -370,11 +371,15 @@ static void copy_huge_page(struct page *dst, struct page *src,
> {
> int i;
> struct hstate *h = hstate_vma(vma);
> + struct page *dst_base = dst;
> + struct page *src_base = src;
>
> might_sleep();
> - for (i = 0; i < pages_per_huge_page(h); i++) {
> + for (i = 0; i < pages_per_huge_page(h); i++,
> + dst = mem_map_next(dst, dst_base, i),
> + src = mem_map_next(src, src_base, i)) {
> cond_resched();
> - copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma);
> + copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);
> }
> }
>
> @@ -2103,7 +2108,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> same_page:
> if (pages) {
> get_page(page);
> - pages[i] = page + pfn_offset;
> + pages[i] = mem_map_offset(page, pfn_offset);
> }
>
> if (vmas)
> diff --git a/mm/internal.h b/mm/internal.h
> index 1f43f74..08b8dea 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -53,6 +53,34 @@ static inline unsigned long page_order(struct page *page)
> }
>
> /*
> + * Return the mem_map entry representing the 'offset' subpage within
> + * the maximally aligned gigantic page 'base'. Handle any discontiguity
> + * in the mem_map at MAX_ORDER_NR_PAGES boundaries.
> + */
> +static inline struct page *mem_map_offset(struct page *base, int offset)
> +{
> + if (unlikely(offset >= MAX_ORDER_NR_PAGES))
> + return pfn_to_page(page_to_pfn(base) + offset);
> + return base + offset;
> +}
> +
> +/*
> + * Iterator over all subpages withing the maximally aligned gigantic
> + * page 'base'. Handle any discontiguity in the mem_map.
> + */
> +static inline struct page *mem_map_next(struct page *iter,
> + struct page *base, int offset)
> +{
> + if (unlikely((offset & (MAX_ORDER_NR_PAGES - 1)) == 0)) {
> + unsigned long pfn = page_to_pfn(base) + offset;
> + if (!pfn_valid(pfn))
> + return NULL;
> + return pfn_to_page(pfn);
> + }
> + return iter + 1;
> +}
> +
> +/*
> * FLATMEM and DISCONTIGMEM configurations use alloc_bootmem_node,
> * so all functions starting at paging_init should be marked __init
> * in those cases. SPARSEMEM, however, allows for memory hotplug,
> --
> 1.6.0.1.451.gc8d31
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab