mm hugetlb: add hugepage support to pagemap

This patch enables extraction of the pfn of a hugepage from
/proc/pid/pagemap in an architecture independent manner.

Details
-------
My test program (leak_pagemap) works as follows:
 - creat() and mmap() a file on hugetlbfs (file size is 200MB == 100 hugepages,)
 - read()/write() something on it,
 - call page-types with option -p,
 - munmap() and unlink() the file on hugetlbfs

Without my patches
------------------
$ ./leak_pagemap
             flags page-count       MB  symbolic-flags                     long-symbolic-flags
0x0000000000000000          1        0  __________________________________
0x0000000000000804          1        0  __R________M______________________ referenced,mmap
0x000000000000086c         81        0  __RU_lA____M______________________ referenced,uptodate,lru,active,mmap
0x0000000000005808          5        0  ___U_______Ma_b___________________ uptodate,mmap,anonymous,swapbacked
0x0000000000005868         12        0  ___U_lA____Ma_b___________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c          1        0  __RU_lA____Ma_b___________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
             total        101        0

The output of page-types don't show any hugepage.

With my patches
---------------
$ ./leak_pagemap
             flags page-count       MB  symbolic-flags                     long-symbolic-flags
0x0000000000000000          1        0  __________________________________
0x0000000000030000      51100      199  ________________TG________________ compound_tail,huge
0x0000000000028018        100        0  ___UD__________H_G________________ uptodate,dirty,compound_head,huge
0x0000000000000804          1        0  __R________M______________________ referenced,mmap
0x000000000000080c          1        0  __RU_______M______________________ referenced,uptodate,mmap
0x000000000000086c         80        0  __RU_lA____M______________________ referenced,uptodate,lru,active,mmap
0x0000000000005808          4        0  ___U_______Ma_b___________________ uptodate,mmap,anonymous,swapbacked
0x0000000000005868         12        0  ___U_lA____Ma_b___________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c          1        0  __RU_lA____Ma_b___________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
             total      51300      200

The output of page-types shows 51200 pages contributing to hugepages,
containing 100 head pages and 51100 tail pages as expected.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 67 insertions, 3 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2a1bef9203c6..47c03f4336b8 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -650,6 +650,50 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         return err;
 }
 
+static u64 huge_pte_to_pagemap_entry(pte_t pte, int offset)
+{
+        u64 pme = 0;
+        if (pte_present(pte))
+                pme = PM_PFRAME(pte_pfn(pte) + offset)
+                        | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
+        return pme;
+}
+
+static int pagemap_hugetlb_range(pte_t *pte, unsigned long addr,
+                                 unsigned long end, struct mm_walk *walk)
+{
+        struct vm_area_struct *vma;
+        struct pagemapread *pm = walk->private;
+        struct hstate *hs = NULL;
+        int err = 0;
+
+        vma = find_vma(walk->mm, addr);
+        if (vma)
+                hs = hstate_vma(vma);
+        for (; addr != end; addr += PAGE_SIZE) {
+                u64 pfn = PM_NOT_PRESENT;
+
+                if (vma && (addr >= vma->vm_end)) {
+                        vma = find_vma(walk->mm, addr);
+                        if (vma)
+                                hs = hstate_vma(vma);
+                }
+
+                if (vma && (vma->vm_start <= addr) && is_vm_hugetlb_page(vma)) {
+                        /* calculate pfn of the "raw" page in the hugepage. */
+                        int offset = (addr & ~huge_page_mask(hs)) >> PAGE_SHIFT;
+                        pfn = huge_pte_to_pagemap_entry(*pte, offset);
+                }
+                err = add_to_pagemap(addr, pfn, pm);
+                if (err)
+                        return err;
+        }
+
+        cond_resched();
+
+        return err;
+}
+
 /*
  * /proc/pid/pagemap - an array mapping virtual pages to pfns
  *
@@ -742,6 +786,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 
         pagemap_walk.pmd_entry = pagemap_pte_range;
         pagemap_walk.pte_hole = pagemap_pte_hole;
+        pagemap_walk.hugetlb_entry = pagemap_hugetlb_range;
         pagemap_walk.mm = mm;
         pagemap_walk.private = &pm;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 52b264563cd9..9d65ae4ba0e0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -770,6 +770,7 @@ unsigned long unmap_vmas(struct mmu_gather **tlb,
  * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
  * @pte_entry: if set, called for each non-empty PTE (4th-level) entry
  * @pte_hole: if set, called for each hole at all levels
+ * @hugetlb_entry: if set, called for each hugetlb entry
  *
  * (see walk_page_range for more details)
  */
@@ -779,6 +780,8 @@ struct mm_walk {
         int (*pmd_entry)(pmd_t *, unsigned long, unsigned long, struct mm_walk *);
         int (*pte_entry)(pte_t *, unsigned long, unsigned long, struct mm_walk *);
         int (*pte_hole)(unsigned long, unsigned long, struct mm_walk *);
+        int (*hugetlb_entry)(pte_t *, unsigned long, unsigned long,
+                             struct mm_walk *);
         struct mm_struct *mm;
         void *private;
 };
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index a286915e23ef..7b47a57b6646 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -120,15 +120,31 @@ int walk_page_range(unsigned long addr, unsigned long end,
         do {
                 next = pgd_addr_end(addr, end);
 
-                /* skip hugetlb vma to avoid hugepage PMD being cleared
-                 * in pmd_none_or_clear_bad(). */
+                /*
+                 * 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);
+#ifdef CONFIG_HUGETLB_PAGE
                 if (vma && is_vm_hugetlb_page(vma)) {
+                        pte_t *pte;
+                        struct hstate *hs;
+
                         if (vma->vm_end < next)
                                 next = vma->vm_end;
+                        hs = hstate_vma(vma);
+                        pte = huge_pte_offset(walk->mm,
+                                              addr & huge_page_mask(hs));
+                        if (pte && !huge_pte_none(huge_ptep_get(pte))
+                            && walk->hugetlb_entry)
+                                err = walk->hugetlb_entry(pte, addr,
+                                                          next, walk);
+                        if (err)
+                                break;
                         continue;
                 }
-
+#endif
                 if (pgd_none_or_clear_bad(pgd)) {
                         if (walk->pte_hole)
                                 err = walk->pte_hole(addr, next, walk);