[PATCH 2/3] mincore: Introduce the MINCORE_ANON bit

[Pavel Emelyanov <xemul@parallels.com>]

When creating a memory dump of a running application it is better to have
the smallest possible set of pages. Using the existing mincore() bit helps,
but not much -- it repotes pages from page cache, which have not necessarily
being mapped by an application, and pages from private file mappings, that
are not yet being cow-ed and thus their contents doesn't differ from file.

Introduce the 2nd bit of mincore, that reports whether a page is not backed
by a file on disk. I.e. all pages from anonymous mappings and those pages
from private file mappings, that have already being cow-ed by write.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

---
 include/linux/mman.h |    1 +
 mm/mincore.c         |   15 +++++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index e4fda1e..9d1de16 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -11,6 +11,7 @@
 #define OVERCOMMIT_NEVER		2
 
 #define MINCORE_RESIDENT	0x1
+#define MINCORE_ANON		0x2
 
 #ifdef __KERNEL__
 #include <linux/mm.h>
diff --git a/mm/mincore.c b/mm/mincore.c
index b719cdd..3163dfb 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -38,7 +38,7 @@ static void mincore_hugetlb_page_range(struct vm_area_struct *vma,
 				       addr & huge_page_mask(h));
 		present = ptep && !huge_pte_none(huge_ptep_get(ptep));
 		while (1) {
-			*vec = (present ? MINCORE_RESIDENT : 0);
+			*vec = (present ? MINCORE_RESIDENT : 0) | MINCORE_ANON;
 			vec++;
 			addr += PAGE_SIZE;
 			if (addr == end)
@@ -86,6 +86,17 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
 	return present ? MINCORE_RESIDENT : 0;
 }
 
+static unsigned char mincore_pte(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
+{
+	struct page *pg;
+
+	pg = vm_normal_page(vma, addr, pte);
+	if (!pg)
+		return 0;
+	else
+		return PageAnon(pg) ? MINCORE_ANON : 0;
+}
+
 static void mincore_unmapped_range(struct vm_area_struct *vma,
 				unsigned long addr, unsigned long end,
 				unsigned char *vec)
@@ -122,7 +133,7 @@ static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		if (pte_none(pte))
 			mincore_unmapped_range(vma, addr, next, vec);
 		else if (pte_present(pte))
-			*vec = MINCORE_RESIDENT;
+			*vec = MINCORE_RESIDENT | mincore_pte(vma, addr, pte);
 		else if (pte_file(pte)) {
 			pgoff = pte_to_pgoff(pte);
 			*vec = mincore_page(vma->vm_file->f_mapping, pgoff);
-- 
1.5.5.6

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