mm: add a field to store names for private anonymous memory

Userspace processes often have multiple allocators that each do
anonymous mmaps to get memory.  When examining memory usage of
individual processes or systems as a whole, it is useful to be
able to break down the various heaps that were allocated by
each layer and examine their size, RSS, and physical memory
usage.

This patch adds a user pointer to the shared union in
vm_area_struct that points to a null terminated string inside
the user process containing a name for the vma.  vmas that
point to the same address will be merged, but vmas that
point to equivalent strings at different addresses will
not be merged.

Userspace can set the name for a region of memory by calling
prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
Setting the name to NULL clears it.

The names of named anonymous vmas are shown in /proc/pid/maps
as [anon:<name>] and in /proc/pid/smaps in a new "Name" field
that is only present for named vmas.  If the userspace pointer
is no longer valid all or part of the name will be replaced
with "<fault>".

The idea to store a userspace pointer to reduce the complexity
within mm (at the expense of the complexity of reading
/proc/pid/mem) came from Dave Hansen.  This results in no
runtime overhead in the mm subsystem other than comparing
the anon_name pointers when considering vma merging.  The pointer
is stored in a union with fieds that are only used on file-backed
mappings, so it does not increase memory usage.

Change-Id: I53b093d98dc24f41377824f34e076edced4a6f07

5 files changed, 35 insertions, 23 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index deabe5f603a..5a273afd199 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -87,7 +87,8 @@ 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));
+				vma->vm_file, pgoff, vma_policy(vma),
+				vma_get_anon_name(vma));
 	if (*prev) {
 		vma = *prev;
 		goto success;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7065fb3a2b4..7c8caa9bc0a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -664,8 +664,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
 		vmend   = min(end, vma->vm_end);
 
 		pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
-		prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
-				  vma->anon_vma, vma->vm_file, pgoff, new_pol);
+                prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
+                                 vma->anon_vma, vma->vm_file, pgoff,
+                                 new_pol, vma_get_anon_name(name));
 		if (prev) {
 			vma = prev;
 			next = vma->vm_next;
diff --git a/mm/mlock.c b/mm/mlock.c
index b41b3b7788f..734fd7f08f9 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -321,7 +321,8 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 
 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 	*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
-			  vma->vm_file, pgoff, vma_policy(vma));
+			  vma->vm_file, pgoff, vma_policy(vma),
+			  vma_get_anon_name(vma));
 	if (*prev) {
 		vma = *prev;
 		goto success;
diff --git a/mm/mmap.c b/mm/mmap.c
index d1cf520e511..96f124e15a8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -656,7 +656,8 @@ again:			remove_next = 1 + (end > next->vm_end);
  * per-vma resources, so we don't attempt to merge those.
  */
 static inline int is_mergeable_vma(struct vm_area_struct *vma,
-			struct file *file, unsigned long vm_flags)
+			struct file *file, unsigned long vm_flags,
+			const char __user *anon_name)
 {
 	/* VM_CAN_NONLINEAR may get set later by f_op->mmap() */
 	if ((vma->vm_flags ^ vm_flags) & ~VM_CAN_NONLINEAR)
@@ -665,6 +666,8 @@ 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_get_anon_name(vma) != anon_name)
+		return 0;
 	return 1;
 }
 
@@ -695,9 +698,10 @@ static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
  */
 static int
 can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
-	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
+	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff,
+	const char __user *anon_name)
 {
-	if (is_mergeable_vma(vma, file, vm_flags) &&
+	if (is_mergeable_vma(vma, file, vm_flags, anon_name) &&
 	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		if (vma->vm_pgoff == vm_pgoff)
 			return 1;
@@ -714,9 +718,10 @@ can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
  */
 static int
 can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
-	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
+	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff,
+	const char __user *anon_name)
 {
-	if (is_mergeable_vma(vma, file, vm_flags) &&
+	if (is_mergeable_vma(vma, file, vm_flags, anon_name) &&
 	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		pgoff_t vm_pglen;
 		vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
@@ -727,9 +732,9 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
 }
 
 /*
- * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
- * whether that can be merged with its predecessor or its successor.
- * Or both (it neatly fills a hole).
+ * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
+ * figure out whether that can be merged with its predecessor or its
+ * successor.  Or both (it neatly fills a hole).
  *
  * In most cases - when called for mmap, brk or mremap - [addr,end) is
  * certain not to be mapped by the time vma_merge is called; but when
@@ -759,7 +764,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 			struct vm_area_struct *prev, unsigned long addr,
 			unsigned long end, unsigned long vm_flags,
 		     	struct anon_vma *anon_vma, struct file *file,
-			pgoff_t pgoff, struct mempolicy *policy)
+			pgoff_t pgoff, struct mempolicy *policy,
+			const char __user *anon_name)
 {
 	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
 	struct vm_area_struct *area, *next;
@@ -785,15 +791,15 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 	 */
 	if (prev && prev->vm_end == addr &&
   			mpol_equal(vma_policy(prev), policy) &&
-			can_vma_merge_after(prev, vm_flags,
-						anon_vma, file, pgoff)) {
+			can_vma_merge_after(prev, vm_flags, anon_vma,
+						file, pgoff, anon_name)) {
 		/*
 		 * OK, it can.  Can we now merge in the successor as well?
 		 */
 		if (next && end == next->vm_start &&
 				mpol_equal(policy, vma_policy(next)) &&
-				can_vma_merge_before(next, vm_flags,
-					anon_vma, file, pgoff+pglen) &&
+				can_vma_merge_before(next, vm_flags, anon_vma,
+						file, pgoff+pglen, anon_name) &&
 				is_mergeable_anon_vma(prev->anon_vma,
 						      next->anon_vma, NULL)) {
 							/* cases 1, 6 */
@@ -813,8 +819,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 	 */
 	if (next && end == next->vm_start &&
  			mpol_equal(policy, vma_policy(next)) &&
-			can_vma_merge_before(next, vm_flags,
-					anon_vma, file, pgoff+pglen)) {
+			can_vma_merge_before(next, vm_flags, anon_vma,
+					file, pgoff+pglen, anon_name)) {
 		if (prev && addr < prev->vm_end)	/* case 4 */
 			err = vma_adjust(prev, prev->vm_start,
 				addr, prev->vm_pgoff, NULL);
@@ -1251,7 +1257,8 @@ munmap_back:
 	/*
 	 * Can we just expand an old mapping?
 	 */
-	vma = vma_merge(mm, prev, addr, addr + len, vm_flags, NULL, file, pgoff, NULL);
+	vma = vma_merge(mm, prev, addr, addr + len, vm_flags, NULL, file, pgoff,
+			NULL, NULL);
 	if (vma)
 		goto out;
 
@@ -2202,7 +2209,7 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
 
 	/* Can we just expand an old private anonymous mapping? */
 	vma = vma_merge(mm, prev, addr, addr + len, flags,
-					NULL, NULL, pgoff, NULL);
+					NULL, NULL, pgoff, NULL, NULL);
 	if (vma)
 		goto out;
 
@@ -2340,7 +2347,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 
 	find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
 	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
-			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
+			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
+			vma_get_anon_name(vma));
 	if (new_vma) {
 		/*
 		 * Source vma may have been merged into new_vma
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 5a688a2756b..5f168ebd9fb 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -179,7 +179,8 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 	 */
 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 	*pprev = vma_merge(mm, *pprev, start, end, newflags,
-			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
+			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
+			vma_get_anon_name(vma));
 	if (*pprev) {
 		vma = *pprev;
 		goto success;