Commit ad820c5d authored Mar 06, 2006 by Nick Piggin Committed by Linus Torvalds Mar 06, 2006

[PATCH] smaps: shared fix

The point of the smaps "shared" is to count the number of pages that are
mapped by more than one process, according to Mauricio Lin. However, smaps
uses page_count for this, so it will return a false positive for every page
that is mapped by just that one process, which is also in pagecache or
swapcache. There are false positive situations for anonymous pages not in
swapcache as well: - page reclaim, migration - get_user_pages (eg.
direct-io, ptrace)

Use page_mapcount instead, to count the number of mappings to the page.

Use vm_normal_page so that weird things like /dev/mem aren't counted either.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 5ddfae16

fs/proc/task_mmu.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -204,7 +204,6 @@ static void smaps_pte_range(struct vm_area_struct vma, pmd_t pmd,
		{
		pte_t *pte, ptent;
		spinlock_t *ptl;
		unsigned long pfn;
		struct page *page;

		pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
		@@ -214,12 +213,12 @@ static void smaps_pte_range(struct vm_area_struct vma, pmd_t pmd,
		continue;

		mss->resident += PAGE_SIZE;
		pfn = pte_pfn(ptent);
		if (!pfn_valid(pfn))

		page = vm_normal_page(vma, addr, ptent);
		if (!page)
		continue;

		page = pfn_to_page(pfn);
		if (page_count(page) >= 2) {
		if (page_mapcount(page) >= 2) {
		if (pte_dirty(ptent))
		mss->shared_dirty += PAGE_SIZE;
		else

Admin message