pagemap: add mmap-exclusive bit for marking pages mapped only here

This patch sets bit 56 in pagemap if this page is mapped only once.  It
allows to detect exclusively used pages without exposing PFN:

present file exclusive state
0       0    0         non-present
1       1    0         file page mapped somewhere else
1       1    1         file page mapped only here
1       0    0         anon non-CoWed page (shared with parent/child)
1       0    1         anon CoWed page (or never forked)

CoWed pages in (MAP_FILE | MAP_PRIVATE) areas are anon in this context.

MMap-exclusive bit doesn't reflect potential page-sharing via swapcache:
page could be mapped once but has several swap-ptes which point to it.
Application could detect that by swap bit in pagemap entry and touch that
pte via /proc/pid/mem to get real information.

See http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com

Requested by Mark Williamson.

[akpm@linux-foundation.org: fix spello]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Mark Williamson <mwilliamson@undo-software.com>
Tested-by:  Mark Williamson <mwilliamson@undo-software.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 603ec916716b..7f73fa32a590 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -62,6 +62,7 @@
 #define PM_PFRAME_MASK          ((1LL << PM_PFRAME_BITS) - 1)
 #define PM_PFRAME(x)            ((x) & PM_PFRAME_MASK)
 #define PM_SOFT_DIRTY           (1ULL << 55)
+#define PM_MMAP_EXCLUSIVE       (1ULL << 56)
 #define PM_FILE                 (1ULL << 61)
 #define PM_SWAP                 (1ULL << 62)
 #define PM_PRESENT              (1ULL << 63)
@@ -91,6 +92,8 @@
 #define KPF_SLOB_FREE           49
 #define KPF_SLUB_FROZEN         50
 #define KPF_SLUB_DEBUG          51
+#define KPF_FILE                62
+#define KPF_MMAP_EXCLUSIVE      63
 
 #define KPF_ALL_BITS            ((uint64_t)~0ULL)
 #define KPF_HACKERS_BITS        (0xffffULL << 32)
@@ -140,6 +143,9 @@ static const char * const page_flag_names[] = {
         [KPF_SLOB_FREE]         = "P:slob_free",
         [KPF_SLUB_FROZEN]       = "A:slub_frozen",
         [KPF_SLUB_DEBUG]        = "E:slub_debug",
+
+        [KPF_FILE]              = "F:file",
+        [KPF_MMAP_EXCLUSIVE]    = "1:mmap_exclusive",
 };
 
 
@@ -443,6 +449,10 @@ static uint64_t expand_overloaded_flags(uint64_t flags, uint64_t pme)
 
         if (pme & PM_SOFT_DIRTY)
                 flags |= BIT(SOFTDIRTY);
+        if (pme & PM_FILE)
+                flags |= BIT(FILE);
+        if (pme & PM_MMAP_EXCLUSIVE)
+                flags |= BIT(MMAP_EXCLUSIVE);
 
         return flags;
 }