[PATCH] mbind: check_range use standard ptwalk

Strict mbind's check for currently mapped pages being on node has been
using a slow loop which re-evaluates pgd, pud, pmd, pte for each entry:
replace that by a standard four-level page table walk like others in mm.
Since mmap_sem is held for writing, page_table_lock can be taken at the
inner level to limit latency.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 70 insertions, 45 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c512cc911e22..cb41c31e7c87 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -238,56 +238,81 @@ static struct mempolicy *mpol_new(int mode, unsigned long *nodes)
 }
 
 /* Ensure all existing pages follow the policy. */
-static int
-verify_pages(struct mm_struct *mm,
-             unsigned long addr, unsigned long end, unsigned long *nodes)
+static int check_pte_range(struct mm_struct *mm, pmd_t *pmd,
+                unsigned long addr, unsigned long end, unsigned long *nodes)
 {
-        int err = 0;
+        pte_t *orig_pte;
+        pte_t *pte;
 
         spin_lock(&mm->page_table_lock);
-        while (addr < end) {
-                struct page *p;
-                pte_t *pte;
-                pmd_t *pmd;
-                pud_t *pud;
-                pgd_t *pgd;
-                pgd = pgd_offset(mm, addr);
-                if (pgd_none(*pgd)) {
-                        unsigned long next = (addr + PGDIR_SIZE) & PGDIR_MASK;
-                        if (next > addr)
-                                break;
-                        addr = next;
-                        continue;
-                }
-                pud = pud_offset(pgd, addr);
-                if (pud_none(*pud)) {
-                        addr = (addr + PUD_SIZE) & PUD_MASK;
+        orig_pte = pte = pte_offset_map(pmd, addr);
+        do {
+                unsigned long pfn;
+                unsigned int nid;
+
+                if (!pte_present(*pte))
                         continue;
-                }
-                pmd = pmd_offset(pud, addr);
-                if (pmd_none(*pmd)) {
-                        addr = (addr + PMD_SIZE) & PMD_MASK;
+                pfn = pte_pfn(*pte);
+                if (!pfn_valid(pfn))
                         continue;
-                }
-                p = NULL;
-                pte = pte_offset_map(pmd, addr);
-                if (pte_present(*pte)) {
-                        unsigned long pfn = pte_pfn(*pte);
-                        if (pfn_valid(pfn))
-                                p = pfn_to_page(pfn);
-                }
-                pte_unmap(pte);
-                if (p) {
-                        unsigned nid = page_to_nid(p);
-                        if (!test_bit(nid, nodes)) {
-                                err = -EIO;
-                                break;
-                        }
-                }
-                addr += PAGE_SIZE;
-        }
+                nid = pfn_to_nid(pfn);
+                if (!test_bit(nid, nodes))
+                        break;
+        } while (pte++, addr += PAGE_SIZE, addr != end);
+        pte_unmap(orig_pte);
         spin_unlock(&mm->page_table_lock);
-        return err;
+        return addr != end;
+}
+
+static inline int check_pmd_range(struct mm_struct *mm, pud_t *pud,
+                unsigned long addr, unsigned long end, unsigned long *nodes)
+{
+        pmd_t *pmd;
+        unsigned long next;
+
+        pmd = pmd_offset(pud, addr);
+        do {
+                next = pmd_addr_end(addr, end);
+                if (pmd_none_or_clear_bad(pmd))
+                        continue;
+                if (check_pte_range(mm, pmd, addr, next, nodes))
+                        return -EIO;
+        } while (pmd++, addr = next, addr != end);
+        return 0;
+}
+
+static inline int check_pud_range(struct mm_struct *mm, pgd_t *pgd,
+                unsigned long addr, unsigned long end, unsigned long *nodes)
+{
+        pud_t *pud;
+        unsigned long next;
+
+        pud = pud_offset(pgd, addr);
+        do {
+                next = pud_addr_end(addr, end);
+                if (pud_none_or_clear_bad(pud))
+                        continue;
+                if (check_pmd_range(mm, pud, addr, next, nodes))
+                        return -EIO;
+        } while (pud++, addr = next, addr != end);
+        return 0;
+}
+
+static inline int check_pgd_range(struct mm_struct *mm,
+                unsigned long addr, unsigned long end, unsigned long *nodes)
+{
+        pgd_t *pgd;
+        unsigned long next;
+
+        pgd = pgd_offset(mm, addr);
+        do {
+                next = pgd_addr_end(addr, end);
+                if (pgd_none_or_clear_bad(pgd))
+                        continue;
+                if (check_pud_range(mm, pgd, addr, next, nodes))
+                        return -EIO;
+        } while (pgd++, addr = next, addr != end);
+        return 0;
 }
 
 /* Step 1: check the range */
@@ -308,7 +333,7 @@ check_range(struct mm_struct *mm, unsigned long start, unsigned long end,
                 if (prev && prev->vm_end < vma->vm_start)
                         return ERR_PTR(-EFAULT);
                 if ((flags & MPOL_MF_STRICT) && !is_vm_hugetlb_page(vma)) {
-                        err = verify_pages(vma->vm_mm,
+                        err = check_pgd_range(vma->vm_mm,
                                            vma->vm_start, vma->vm_end, nodes);
                         if (err) {
                                 first = ERR_PTR(err);