[patch 09/49] hugetlbfs: handle pages higher order than MAX_ORDER

Greg KH
2008-11-12T00:29:34Z

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2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Andy Whitcroft <apw@shadowen.org>

commit 69d177c2fc702d402b17fdca2190d5a7e3ca55c5 upstream

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 to
implement gigantic page versions of copy_huge_page and clear_huge_page,
and to allow follow_hugetlb_page handle gigantic pages.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Cc: Jon Tollefson <kniht@linux.vnet.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

---
mm/hugetlb.c | 37 ++++++++++++++++++++++++++++++++++++-
mm/internal.h | 28 ++++++++++++++++++++++++++++
2 files changed, 64 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -353,11 +353,26 @@ static int vma_has_reserves(struct vm_ar
return 0;
}

+static void clear_gigantic_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++, p = mem_map_next(p, page, i)) {
+ cond_resched();
+ clear_user_highpage(p, addr + i * PAGE_SIZE);
+ }
+}
static void clear_huge_page(struct page *page,
unsigned long addr, unsigned long sz)
{
int i;

+ if (unlikely(sz > MAX_ORDER_NR_PAGES))
+ return clear_gigantic_page(page, addr, sz);
+
might_sleep();
for (i = 0; i < sz/PAGE_SIZE; i++) {
cond_resched();
@@ -365,12 +380,32 @@ static void clear_huge_page(struct page
}
}

+static void copy_gigantic_page(struct page *dst, struct page *src,
+ unsigned long addr, struct vm_area_struct *vma)
+{
+ 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); ) {
+ cond_resched();
+ copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);
+
+ i++;
+ dst = mem_map_next(dst, dst_base, i);
+ src = mem_map_next(src, src_base, i);
+ }
+}
static void copy_huge_page(struct page *dst, struct page *src,
unsigned long addr, struct vm_area_struct *vma)
{
int i;
struct hstate *h = hstate_vma(vma);

+ if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES))
+ return copy_gigantic_page(dst, src, addr, vma);
+
might_sleep();
for (i = 0; i < pages_per_huge_page(h); i++) {
cond_resched();
@@ -2113,7 +2148,7 @@ int follow_hugetlb_page(struct mm_struct
same_page:
if (pages) {
get_page(page);
- pages[i] = page + pfn_offset;
+ pages[i] = mem_map_offset(page, pfn_offset);
}

if (vmas)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -54,6 +54,34 @@ static inline unsigned long page_order(s
}

/*
+ * 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,

--