mm: introduce MMF_VM_PREFERRDED flag

From: Konstantin Khlebnikov <khlebnikov@openvz.org>

This patch introduce mm->flags bit: MMF_VM_PREFERRED,
which doubles access bit weight for this mm.

Currently the only one effect:
mm with this bit activates mapped file pages after first touch,
if vma does not marked as sequentially accessed.

This should be per-vma sign, but there no free bits in vma->vm_flags,
maybe we can make this stuff 64-only.

interface:
prctl(PR_SET_MM_PREFERRED, 1) to set and
prctl(PR_SET_MM_PREFERRED, 0) to clear.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 include/linux/prctl.h |    2 ++
 include/linux/sched.h |    1 +
 kernel/sys.c          |   17 +++++++++++++++++
 mm/rmap.c             |    5 ++++-
 4 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 7ddc7f1..d0f9ceb 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -114,4 +114,6 @@
 # define PR_SET_MM_START_BRK		6
 # define PR_SET_MM_BRK			7
 
+#define PR_SET_MM_PREFERRED	36
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 75c15c5..b60883a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -437,6 +437,7 @@ extern int get_dumpable(struct mm_struct *mm);
 					/* leave room for more dump flags */
 #define MMF_VM_MERGEABLE	16	/* KSM may merge identical pages */
 #define MMF_VM_HUGEPAGE		17	/* set when VM_HUGEPAGE is set on vma */
+#define MMF_VM_PREFERRED	18	/* Double pte access bits weight */
 
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
diff --git a/kernel/sys.c b/kernel/sys.c
index 4070153..bacf8d5 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1810,6 +1810,20 @@ static int prctl_set_mm(int opt, unsigned long addr,
 }
 #endif
 
+static int set_mm_preferred(struct mm_struct *mm, int state)
+{
+	switch (state) {
+		case 0:
+			clear_bit(MMF_VM_PREFERRED, &mm->flags);
+			return 0;
+		case 1:
+			set_bit(MMF_VM_PREFERRED, &mm->flags);
+			return 0;
+		default:
+			return -EINVAL;
+	}
+}
+
 SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		unsigned long, arg4, unsigned long, arg5)
 {
@@ -1962,6 +1976,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		case PR_SET_MM:
 			error = prctl_set_mm(arg2, arg3, arg4, arg5);
 			break;
+		case PR_SET_MM_PREFERRED:
+			error = set_mm_preferred(me->mm, arg2);
+			break;
 		default:
 			error = -EINVAL;
 			break;
diff --git a/mm/rmap.c b/mm/rmap.c
index 78cc46b..b0fd1d1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -766,8 +766,11 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 
 	(*mapcount)--;
 
-	if (referenced)
+	if (referenced) {
+		if (test_bit(MMF_VM_PREFERRED, &mm->flags))
+			referenced <<= 1;
 		*vm_flags |= vma->vm_flags;
+	}
 out:
 	return referenced;
 }