[PATCH 2/3] Helper which returns the huge page at a given address (Take 3)

[Alexey Korolev <akorolex@gmail.com>]

This patch provides helper function which returns the huge page at a
given address for population before the page has been faulted.
It is possible to call hugetlb_get_user_page function in file mmap
procedure to get pages before they have been requested by user level.

include/linux/hugetlb.h |    3 +++
mm/hugetlb.c            |   23 +++++++++++++++++++++++
2 files changed, 26 insertions(+)

---
Signed-off-by: Alexey Korolev <akorolev@infradead.org>

diff -aurp clean/include/linux/hugetlb.h patched/include/linux/hugetlb.h
--- clean/include/linux/hugetlb.h	2009-09-11 15:33:48.000000000 +1200
+++ patched/include/linux/hugetlb.h	2009-09-11 20:09:02.000000000 +1200
@@ -39,6 +39,8 @@ int hugetlb_reserve_pages(struct inode *
 						struct vm_area_struct *vma,
 						int acctflags);
 void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed);
+struct page *hugetlb_get_user_page(struct vm_area_struct *vma,
+						unsigned long address);

 extern unsigned long hugepages_treat_as_movable;
 extern const unsigned long hugetlb_zero, hugetlb_infinity;
@@ -100,6 +102,7 @@ static inline void hugetlb_report_meminf
 #define is_hugepage_only_range(mm, addr, len)	0
 #define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; })
 #define hugetlb_fault(mm, vma, addr, flags)	({ BUG(); 0; })
+#define hugetlb_get_user_page(vma, address)	ERR_PTR(-EINVAL)

 #define hugetlb_change_protection(vma, address, end, newprot)

diff -aurp clean/mm/hugetlb.c patched/mm/hugetlb.c
--- clean/mm/hugetlb.c	2009-09-06 11:38:12.000000000 +1200
+++ patched/mm/hugetlb.c	2009-09-11 08:34:00.000000000 +1200
@@ -2187,6 +2187,29 @@ static int huge_zeropage_ok(pte_t *ptep,
 		return huge_pte_none(huge_ptep_get(ptep));
 }

+/*
+ * hugetlb_get_user_page returns the page at a given address for population
+ * before the page has been faulted.
+ */
+struct page *hugetlb_get_user_page(struct vm_area_struct *vma,
+				    unsigned long address)
+{
+	int ret;
+	int cnt = 1;
+	struct page *pg;
+	struct hstate *h = hstate_vma(vma);
+
+	address = address & huge_page_mask(h);
+	ret = follow_hugetlb_page(vma->vm_mm, vma, &pg,
+				NULL, &address, &cnt, 0, 0);
+	if (ret < 0)
+		return ERR_PTR(ret);
+	put_page(pg);
+
+	return pg;
+}
+EXPORT_SYMBOL_GPL(hugetlb_get_user_page);
+
 int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			struct page **pages, struct vm_area_struct **vmas,
 			unsigned long *position, int *length, int i,

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