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Subject[PATCH 1/3] hugetlb: Remove get_user_pages optimization
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Version 2 (Mon, 3 Oct 2005)
* Removed follow_hugetlb_page since get_user_pages() was the only caller.

Initial Post (Thu, 18 Aug 2005)

In preparation for hugetlb demand faulting, remove this get_user_pages()
optimization. Since huge pages will no longer be prefaulted, we can't assume
that the huge ptes are established and hence, calling follow_hugetlb_page() is
not valid.

With the follow_hugetlb_page() call removed, the normal code path will be
triggered. follow_page() will either use follow_huge_addr() or
follow_huge_pmd() to check for a previously faulted "page" to return. When
this fails (ie. with demand faults), __handle_mm_fault() gets called which
invokes the hugetlb_fault() handler to instantiate the huge page.

This patch doesn't make a lot of sense by itself, but I've broken it out to
facilitate discussion on this specific element of the demand fault changes.
While coding this up, I referenced previous discussion on this topic starting
at http://lkml.org/lkml/2004/4/13/176 , which contains more opinions about the
correctness of this approach.

Signed-off-by: Adam Litke <agl@us.ibm.com>

---
hugetlb.c | 54 ------------------------------------------------------
memory.c | 5 -----
2 files changed, 59 deletions(-)
diff -upN reference/mm/hugetlb.c current/mm/hugetlb.c
--- reference/mm/hugetlb.c
+++ current/mm/hugetlb.c
@@ -392,57 +392,3 @@ out:
spin_unlock(&mm->page_table_lock);
return ret;
}
-
-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)
-{
- unsigned long vpfn, vaddr = *position;
- int remainder = *length;
-
- BUG_ON(!is_vm_hugetlb_page(vma));
-
- vpfn = vaddr/PAGE_SIZE;
- spin_lock(&mm->page_table_lock);
- while (vaddr < vma->vm_end && remainder) {
-
- if (pages) {
- pte_t *pte;
- struct page *page;
-
- /* Some archs (sparc64, sh*) have multiple
- * pte_ts to each hugepage. We have to make
- * sure we get the first, for the page
- * indexing below to work. */
- pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);
-
- /* the hugetlb file might have been truncated */
- if (!pte || pte_none(*pte)) {
- remainder = 0;
- if (!i)
- i = -EFAULT;
- break;
- }
-
- page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];
-
- WARN_ON(!PageCompound(page));
-
- get_page(page);
- pages[i] = page;
- }
-
- if (vmas)
- vmas[i] = vma;
-
- vaddr += PAGE_SIZE;
- ++vpfn;
- --remainder;
- ++i;
- }
- spin_unlock(&mm->page_table_lock);
- *length = remainder;
- *position = vaddr;
-
- return i;
-}
diff -upN reference/mm/memory.c current/mm/memory.c
--- reference/mm/memory.c
+++ current/mm/memory.c
@@ -971,11 +971,6 @@ int get_user_pages(struct task_struct *t
|| !(flags & vma->vm_flags))
return i ? : -EFAULT;

- if (is_vm_hugetlb_page(vma)) {
- i = follow_hugetlb_page(mm, vma, pages, vmas,
- &start, &len, i);
- continue;
- }
spin_lock(&mm->page_table_lock);
do {
int write_access = write;
--
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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