Re: [PATCH 1/3 htlb-get_user_pages] Demand faulting for huge pages

From: Adam Litke (agl_at_us.ibm.com)
Date: 09/28/05

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    To: akpm@osdl.org
Date:	Wed, 28 Sep 2005 15:31:18 -0500

    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.

    Diffed against 2.6.14-rc2-git6

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

    ---
 memory.c |    5 -----
 1 files changed, 5 deletions(-)
diff -upN reference/mm/memory.c current/mm/memory.c
--- reference/mm/memory.c
+++ current/mm/memory.c
@@ -949,11 +949,6 @@ 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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