pagewalk: don't look up vma if walk->hugetlb_entry is unused

Currently, walk_page_range() calls find_vma() every page table for walk
iteration.  but it's completely unnecessary if walk->hugetlb_entry is
unused.  And we don't have to assume find_vma() is a lightweight
operation.  So this patch checks the walk->hugetlb_entry and avoids the
find_vma() call if possible.

This patch also makes some cleanups.  1) remove ugly uninitialized_var()
and 2) #ifdef in function body.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 37 insertions, 6 deletions

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 606bbb4125d0..ee4ff87c58c1 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -126,7 +126,39 @@ static int walk_hugetlb_range(struct vm_area_struct *vma,
 
         return 0;
 }
-#endif
+
+static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)
+{
+        struct vm_area_struct *vma;
+
+        /* We don't need vma lookup at all. */
+        if (!walk->hugetlb_entry)
+                return NULL;
+
+        VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
+        vma = find_vma(walk->mm, addr);
+        if (vma && vma->vm_start <= addr && is_vm_hugetlb_page(vma))
+                return vma;
+
+        return NULL;
+}
+
+#else /* CONFIG_HUGETLB_PAGE */
+static struct vm_area_struct* hugetlb_vma(unsigned long addr, struct mm_walk *walk)
+{
+        return NULL;
+}
+
+static int walk_hugetlb_range(struct vm_area_struct *vma,
+                              unsigned long addr, unsigned long end,
+                              struct mm_walk *walk)
+{
+        return 0;
+}
+
+#endif /* CONFIG_HUGETLB_PAGE */
+
+
 
 /**
  * walk_page_range - walk a memory map's page tables with a callback
@@ -165,18 +197,17 @@ int walk_page_range(unsigned long addr, unsigned long end,
 
         pgd = pgd_offset(walk->mm, addr);
         do {
-                struct vm_area_struct *uninitialized_var(vma);
+                struct vm_area_struct *vma;
 
                 next = pgd_addr_end(addr, end);
 
-#ifdef CONFIG_HUGETLB_PAGE
                 /*
                  * handle hugetlb vma individually because pagetable walk for
                  * the hugetlb page is dependent on the architecture and
                  * we can't handled it in the same manner as non-huge pages.
                  */
-                vma = find_vma(walk->mm, addr);
-                if (vma && vma->vm_start <= addr && is_vm_hugetlb_page(vma)) {
+                vma = hugetlb_vma(addr, walk);
+                if (vma) {
                         if (vma->vm_end < next)
                                 next = vma->vm_end;
                         /*
@@ -189,7 +220,7 @@ int walk_page_range(unsigned long addr, unsigned long end,
                         pgd = pgd_offset(walk->mm, next);
                         continue;
                 }
-#endif
+
                 if (pgd_none_or_clear_bad(pgd)) {
                         if (walk->pte_hole)
                                 err = walk->pte_hole(addr, next, walk);