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

[Adam Litke <agl@us.ibm.com>]

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