[RFC] mm:fix zero_page huge_zero_page rss/pss statistic

["Wang, Yalin" <Yalin.Wang@sonymobile.com>]

smaps_pte_entry() doesn't ignore zero_huge_page,
but it ignore zero_page, because vm_normal_page() will
ignore it. We remove vm_normal_page() call, because walk_page_range()
have ignore VM_PFNMAP vma maps, it's safe to just use pfn_valid(),
so that we can also consider zero_page to be a valid page.

Another change is that we only add map_count >= 2 or mapcount == 1
pages into pss, because zero_page and huge_zero_page's _mapcount is
zero, this means pss will consider evey zero page as a PAGE_SIZE for
every process, this is not correct for pss statistic. We ignore
zero page for pss, just add zero page into rss statistic.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 fs/proc/task_mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 4e0388c..ce503d3 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -458,7 +458,9 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
 	int mapcount;
 
 	if (pte_present(ptent)) {
-		page = vm_normal_page(vma, addr, ptent);
+		if (!pte_special(ptent) && pfn_valid(pte_pfn(ptent)))
+			page = pfn_to_page(pte_pfn(ptent));
+
 	} else if (is_swap_pte(ptent)) {
 		swp_entry_t swpent = pte_to_swp_entry(ptent);
 
@@ -491,7 +493,7 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
 		else
 			mss->shared_clean += ptent_size;
 		mss->pss += (ptent_size << PSS_SHIFT) / mapcount;
-	} else {
+	} else if (mapcount == 1){
 		if (pte_dirty(ptent) || PageDirty(page))
 			mss->private_dirty += ptent_size;
 		else
-- 
2.1.3