mm: report the pagesize backing a VMA in /proc/pid/smaps

It is useful to verify a hugepage-aware application is using the expected
pagesizes for its memory regions. This patch creates an entry called
KernelPageSize in /proc/pid/smaps that is the size of page used by the
kernel to back a VMA. The entry is not called PageSize as it is possible
the MMU uses a different size. This extension should not break any sensible
parser that skips lines containing unrecognised information.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: "KOSAKI Motohiro" <kosaki.motohiro@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 23 insertions, 2 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3a8bdd7f5756..41ef5f23e779 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -396,7 +396,8 @@ static int show_smap(struct seq_file *m, void *v)
                    "Private_Clean:  %8lu kB\n"
                    "Private_Dirty:  %8lu kB\n"
                    "Referenced:     %8lu kB\n"
-                   "Swap:           %8lu kB\n",
+                   "Swap:           %8lu kB\n"
+                   "KernelPageSize: %8lu kB\n",
                    (vma->vm_end - vma->vm_start) >> 10,
                    mss.resident >> 10,
                    (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
@@ -405,7 +406,8 @@ static int show_smap(struct seq_file *m, void *v)
                    mss.private_clean >> 10,
                    mss.private_dirty >> 10,
                    mss.referenced >> 10,
-                   mss.swap >> 10);
+                   mss.swap >> 10,
+                   vma_kernel_pagesize(vma) >> 10);
 
         if (m->count < m->size)  /* vma is copied successfully */
                 m->version = (vma != get_gate_vma(task)) ? vma->vm_start : 0;
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index e1c8afc002c0..648e1e25979e 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -233,6 +233,8 @@ static inline unsigned long huge_page_size(struct hstate *h)
         return (unsigned long)PAGE_SIZE << h->order;
 }
 
+extern unsigned long vma_kernel_pagesize(struct vm_area_struct *vma);
+
 static inline unsigned long huge_page_mask(struct hstate *h)
 {
         return h->mask;
@@ -273,6 +275,7 @@ struct hstate {};
 #define hstate_inode(i) NULL
 #define huge_page_size(h) PAGE_SIZE
 #define huge_page_mask(h) PAGE_MASK
+#define vma_kernel_pagesize(v) PAGE_SIZE
 #define huge_page_order(h) 0
 #define huge_page_shift(h) PAGE_SHIFT
 static inline unsigned int pages_per_huge_page(struct hstate *h)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6058b53dcb89..5cb8bc7c80f7 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -220,6 +220,22 @@ static pgoff_t vma_hugecache_offset(struct hstate *h,
 }
 
 /*
+ * Return the size of the pages allocated when backing a VMA. In the majority
+ * cases this will be same size as used by the page table entries.
+ */
+unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
+{
+        struct hstate *hstate;
+
+        if (!is_vm_hugetlb_page(vma))
+                return PAGE_SIZE;
+
+        hstate = hstate_vma(vma);
+
+        return 1UL << (hstate->order + PAGE_SHIFT);
+}
+
+/*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
  * bits of the reservation map pointer, which are always clear due to
  * alignment.