Re: No more bits in vm_area_struct's vm_flags.

[Nigel Cunningham <ncunningham@crca.org.au>]

Hi.

KAMEZAWA Hiroyuki wrote:
> Then, Nigel, you have 2 choices I think.
> 
> (1) don't merge if vm_hints is set  or (2) pass vm_hints to all
> __merge() functions.
> 
> One of above will be accesptable for stakeholders... I personally
> like (1) but just trying (2) may be accepted.
> 
> What I dislike is making vm_flags to be long long ;)

Okay. I've gone for option 1 for now. Here's what I
currently have (compile testing as I write)...



vm_flags in struct vm_area_struct is full. Move some of the less commonly
used flags to a new variable so that other flags that need to be in vm_flags
(because, for example, they need to be in variables that are passed around)
can be added.

Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>
---
 include/linux/mm.h       |   16 ++++++++--------
 include/linux/mm_types.h |    1 +
 mm/madvise.c             |   28 ++++++++++++++++++----------
 mm/mmap.c                |    2 ++
 4 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24c3956..040d0ce 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -85,10 +85,6 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_LOCKED	0x00002000
 #define VM_IO           0x00004000	/* Memory mapped I/O or similar */
 
-					/* Used by sys_madvise() */
-#define VM_SEQ_READ	0x00008000	/* App will access data sequentially */
-#define VM_RAND_READ	0x00010000	/* App will not benefit from clustered reads */
-
 #define VM_DONTCOPY	0x00020000      /* Do not copy this vma on fork */
 #define VM_DONTEXPAND	0x00040000	/* Cannot expand with mremap() */
 #define VM_RESERVED	0x00080000	/* Count as reserved_vm like IO */
@@ -116,11 +112,15 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_STACK_FLAGS	(VM_GROWSDOWN | VM_STACK_DEFAULT_FLAGS | VM_ACCOUNT)
 #endif
 
+					/* Used by sys_madvise() */
+#define VM_SEQ_READ	0x00000001	/* App will access data sequentially */
+#define VM_RAND_READ	0x00000002	/* App will not benefit from clustered reads */
+
 #define VM_READHINTMASK			(VM_SEQ_READ | VM_RAND_READ)
-#define VM_ClearReadHint(v)		(v)->vm_flags &= ~VM_READHINTMASK
-#define VM_NormalReadHint(v)		(!((v)->vm_flags & VM_READHINTMASK))
-#define VM_SequentialReadHint(v)	((v)->vm_flags & VM_SEQ_READ)
-#define VM_RandomReadHint(v)		((v)->vm_flags & VM_RAND_READ)
+#define VM_ClearReadHint(v)		(v)->vm_hints &= ~VM_READHINTMASK
+#define VM_NormalReadHint(v)		(!((v)->vm_hints & VM_READHINTMASK))
+#define VM_SequentialReadHint(v)	((v)->vm_hints & VM_SEQ_READ)
+#define VM_RandomReadHint(v)		((v)->vm_hints & VM_RAND_READ)
 
 /*
  * special vmas that are non-mergable, non-mlock()able
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 84a524a..5c66e3a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -178,6 +178,7 @@ struct vm_area_struct {
 					   units, *not* PAGE_CACHE_SIZE */
 	struct file * vm_file;		/* File we map to (can be NULL). */
 	void * vm_private_data;		/* was vm_pte (shared mem) */
+	unsigned long vm_hints;		/* Hints, see mm.h. */
 	unsigned long vm_truncate_count;/* truncate_count or restart_addr */
 
 #ifndef CONFIG_MMU
diff --git a/mm/madvise.c b/mm/madvise.c
index 35b1479..59a93d3 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -40,19 +40,22 @@ static long madvise_behavior(struct vm_area_struct * vma,
 		     unsigned long start, unsigned long end, int behavior)
 {
 	struct mm_struct * mm = vma->vm_mm;
-	int error = 0;
+	int error = 0, skip_merge = 0;
 	pgoff_t pgoff;
-	unsigned long new_flags = vma->vm_flags;
+	unsigned long new_flags = vma->vm_flags, new_hints = vma->vm_hints;
 
 	switch (behavior) {
 	case MADV_NORMAL:
-		new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
+		new_hints = new_hints & ~VM_RAND_READ & ~VM_SEQ_READ;
+		skip_merge = 1;
 		break;
 	case MADV_SEQUENTIAL:
-		new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
+		new_hints = (new_hints & ~VM_RAND_READ) | VM_SEQ_READ;
+		skip_merge = 1;
 		break;
 	case MADV_RANDOM:
-		new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
+		new_hints = (new_hints & ~VM_SEQ_READ) | VM_RAND_READ;
+		skip_merge = 1;
 		break;
 	case MADV_DONTFORK:
 		new_flags |= VM_DONTCOPY;
@@ -78,11 +81,15 @@ static long madvise_behavior(struct vm_area_struct * vma,
 	}
 
 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
-	*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
-				vma->vm_file, pgoff, vma_policy(vma));
-	if (*prev) {
-		vma = *prev;
-		goto success;
+
+	if (!skip_merge) {
+		*prev = vma_merge(mm, *prev, start, end, new_flags,
+				vma->anon_vma, vma->vm_file, pgoff,
+				vma_policy(vma));
+		if (*prev) {
+			vma = *prev;
+			goto success;
+		}
 	}
 
 	*prev = vma;
@@ -104,6 +111,7 @@ success:
 	 * vm_flags is protected by the mmap_sem held in write mode.
 	 */
 	vma->vm_flags = new_flags;
+	vma->vm_hints = new_hints;
 
 out:
 	if (error == -ENOMEM)
diff --git a/mm/mmap.c b/mm/mmap.c
index 73f5e4b..fb4bf98 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -670,6 +670,8 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma,
 		return 0;
 	if (vma->vm_ops && vma->vm_ops->close)
 		return 0;
+	if (vma->vm_hints)
+		return 0;
 	return 1;
 }
 
-- 
1.6.3.3