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Subject[PATCHv4 2/2] mm: add a field to store names for private anonymous memory
Date
In many userspace applications, and especially in VM based applications
like Android uses heavily, there are multiple different allocators in use.
At a minimum there is libc malloc and the stack, and in many cases there
are libc malloc, the stack, direct syscalls to mmap anonymous memory, and
multiple VM heaps (one for small objects, one for big objects, etc.).
Each of these layers usually has its own tools to inspect its usage;
malloc by compiling a debug version, the VM through heap inspection tools,
and for direct syscalls there is usually no way to track them.

On Android we heavily use a set of tools that use an extended version of
the logic covered in Documentation/vm/pagemap.txt to walk all pages mapped
in userspace and slice their usage by process, shared (COW) vs. unique
mappings, backing, etc. This can account for real physical memory usage
even in cases like fork without exec (which Android uses heavily to share
as many private COW pages as possible between processes), Kernel SamePage
Merging, and clean zero pages. It produces a measurement of the pages
that only exist in that process (USS, for unique), and a measurement of
the physical memory usage of that process with the cost of shared pages
being evenly split between processes that share them (PSS).

If all anonymous memory is indistinguishable then figuring out the real
physical memory usage (PSS) of each heap requires either a pagemap walking
tool that can understand the heap debugging of every layer, or for every
layer's heap debugging tools to implement the pagemap walking logic, in
which case it is hard to get a consistent view of memory across the whole
system.

Tracking the information in userspace leads to all sorts of problems.
It either needs to be stored inside the process, which means every
process has to have an API to export its current heap information upon
request, or it has to be stored externally in a filesystem that
somebody needs to clean up on crashes. It needs to be readable while
the process is still running, so it has to have some sort of
synchronization with every layer of userspace. Efficiently tracking
the ranges requires reimplementing something like the kernel vma
trees, and linking to it from every layer of userspace. It requires
more memory, more syscalls, more runtime cost, and more complexity to
separately track regions that the kernel is already tracking.

This patch adds a field to /proc/pid/maps and /proc/pid/smaps to show a
userspace-provided name for anonymous vmas. The names of named anonymous
vmas are shown in /proc/pid/maps and /proc/pid/smaps as [anon:<name>].

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 name is stored in a user pointer in the shared union in vm_area_struct
that points to a null terminated string inside the user process. vmas
that point to the same address and are otherwise mergeable will be merged,
but vmas that point to equivalent strings at different addresses will not
be merged.

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 fields that are only used on file-backed
mappings, so it does not increase memory usage.

Signed-off-by: Colin Cross <ccross@android.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Rob Landley <rob@landley.net>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Shaohua Li <shli@fusionio.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

v2: updates the commit message to explain in more detail why the
patch is useful.
v3: renames vma_get_anon_name to vma_anon_name
replaces logic in seq_print_vma_name with access_process_vm
removes Name: entry from smaps, it's already on the header line
changes the prctl option number to match what is currently in
use on Android
v4: adds paragraph to commit log on why this is better than tracking
in userspace
squashes fixes from Andrew Morton to fix build error and warning
fix build error reported by Mark Salter when !CONFIG_MMU

Documentation/filesystems/proc.txt | 2 ++
fs/proc/task_mmu.c | 21 +++++++++++++++
include/linux/mm.h | 5 +++-
include/linux/mm_types.h | 15 +++++++++++
include/uapi/linux/prctl.h | 3 +++
kernel/sys.c | 32 ++++++++++++++++++++++
mm/madvise.c | 55 +++++++++++++++++++++++++++++++++++---
mm/mempolicy.c | 2 +-
mm/mlock.c | 3 ++-
mm/mmap.c | 44 +++++++++++++++++-------------
mm/mprotect.c | 3 ++-
11 files changed, 159 insertions(+), 26 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 823c95faebd2..c78e8438ae55 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -369,6 +369,8 @@ is not associated with a file:
[stack:1001] = the stack of the thread with tid 1001
[vdso] = the "virtual dynamic shared object",
the kernel system call handler
+ [anon:<name>] = an anonymous mapping that has been
+ named by userspace

or if empty, the mapping is anonymous.

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 390bdab01c3c..d234ce3fb286 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -91,6 +91,21 @@ static void pad_len_spaces(struct seq_file *m, int len)
seq_printf(m, "%*c", len, ' ');
}

+static void seq_print_vma_name(struct seq_file *m, struct vm_area_struct *vma)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ char anon_name[NAME_MAX + 1];
+ int n;
+
+ n = access_remote_vm(mm, (unsigned long)vma_anon_name(vma),
+ anon_name, NAME_MAX, 0);
+ if (n > 0) {
+ seq_puts(m, "[anon:");
+ seq_write(m, anon_name, strnlen(anon_name, n));
+ seq_putc(m, ']');
+ }
+}
+
#ifdef CONFIG_NUMA
/*
* These functions are for numa_maps but called in generic **maps seq_file
@@ -336,6 +351,12 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
pad_len_spaces(m, len);
seq_printf(m, "[stack:%d]", tid);
}
+ goto done;
+ }
+
+ if (vma_anon_name(vma)) {
+ pad_len_spaces(m, len);
+ seq_print_vma_name(m, vma);
}
}

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8b6e55ee8855..8ce3223335df 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1493,7 +1493,7 @@ extern int vma_adjust(struct vm_area_struct *vma, unsigned long start,
extern struct vm_area_struct *vma_merge(struct mm_struct *,
struct vm_area_struct *prev, unsigned long addr, unsigned long end,
unsigned long vm_flags, struct anon_vma *, struct file *, pgoff_t,
- struct mempolicy *);
+ struct mempolicy *, const char __user *);
extern struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *);
extern int split_vma(struct mm_struct *,
struct vm_area_struct *, unsigned long addr, int new_below);
@@ -1837,5 +1837,8 @@ void __init setup_nr_node_ids(void);
static inline void setup_nr_node_ids(void) {}
#endif

+int madvise_set_anon_name(unsigned long start, unsigned long len_in,
+ unsigned long name_addr);
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index d9851eeb6e1d..611444e7ff84 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -255,6 +255,10 @@ struct vm_area_struct {
* For areas with an address space and backing store,
* linkage into the address_space->i_mmap interval tree, or
* linkage of vma in the address_space->i_mmap_nonlinear list.
+ *
+ * For private anonymous mappings, a pointer to a null terminated string
+ * in the user process containing the name given to the vma, or NULL
+ * if unnamed.
*/
union {
struct {
@@ -262,6 +266,7 @@ struct vm_area_struct {
unsigned long rb_subtree_last;
} linear;
struct list_head nonlinear;
+ const char __user *anon_name;
} shared;

/*
@@ -455,4 +460,14 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
return mm->cpu_vm_mask_var;
}

+
+/* Return the name for an anonymous mapping or NULL for a file-backed mapping */
+static inline const char __user *vma_anon_name(struct vm_area_struct *vma)
+{
+ if (vma->vm_file)
+ return NULL;
+
+ return vma->shared.anon_name;
+}
+
#endif /* _LINUX_MM_TYPES_H */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 289760f424aa..253856a2a8ad 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -149,4 +149,7 @@

#define PR_GET_TID_ADDRESS 40

+#define PR_SET_VMA 0x53564d41
+# define PR_SET_VMA_ANON_NAME 0
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index c18ecca575b4..4ab9b3b66cb1 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1836,6 +1836,35 @@ static int prctl_get_tid_address(struct task_struct *me, int __user **tid_addr)
}
#endif

+#ifdef CONFIG_MMU
+static int prctl_set_vma(unsigned long opt, unsigned long addr,
+ unsigned long len, unsigned long arg)
+{
+ struct mm_struct *mm = current->mm;
+ int error;
+
+ down_write(&mm->mmap_sem);
+
+ switch (opt) {
+ case PR_SET_VMA_ANON_NAME:
+ error = madvise_set_anon_name(addr, len, arg);
+ break;
+ default:
+ error = -EINVAL;
+ }
+
+ up_write(&mm->mmap_sem);
+
+ return error;
+}
+#else /* CONFIG_MMU */
+static int prctl_set_vma(unsigned long opt, unsigned long start,
+ unsigned long len_in, unsigned long arg)
+{
+ return -EINVAL;
+}
+#endif
+
SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
unsigned long, arg4, unsigned long, arg5)
{
@@ -1999,6 +2028,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
return current->no_new_privs ? 1 : 0;
+ case PR_SET_VMA:
+ error = prctl_set_vma(arg2, arg3, arg4, arg5);
+ break;
default:
error = -EINVAL;
break;
diff --git a/mm/madvise.c b/mm/madvise.c
index aa346f87edbb..69702484d406 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -44,20 +44,22 @@ static int madvise_need_mmap_write(int behavior)
*/
static int madvise_update_vma(struct vm_area_struct *vma,
struct vm_area_struct **prev, unsigned long start,
- unsigned long end, unsigned long new_flags)
+ unsigned long end, unsigned long new_flags,
+ const char __user *new_anon_name)
{
struct mm_struct *mm = vma->vm_mm;
pgoff_t pgoff;
int error;

- if (new_flags == vma->vm_flags) {
+ if (new_flags == vma->vm_flags && new_anon_name == vma_anon_name(vma)) {
*prev = vma;
return 0;
}

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),
+ new_anon_name);
if (*prev) {
vma = *prev;
goto success;
@@ -82,10 +84,30 @@ success:
* vm_flags is protected by the mmap_sem held in write mode.
*/
vma->vm_flags = new_flags;
+ if (!vma->vm_file)
+ vma->shared.anon_name = new_anon_name;

return 0;
}

+static int madvise_vma_anon_name(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end,
+ unsigned long name_addr)
+{
+ int error;
+
+ /* Only anonymous mappings can be named */
+ if (vma->vm_file)
+ return -EINVAL;
+
+ error = madvise_update_vma(vma, prev, start, end, vma->vm_flags,
+ (const char __user *)name_addr);
+ if (error == -ENOMEM)
+ error = -EAGAIN;
+ return error;
+}
+
#ifdef CONFIG_SWAP
static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
unsigned long end, struct mm_walk *walk)
@@ -352,7 +374,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
break;
}

- error = madvise_update_vma(vma, prev, start, end, new_flags);
+ error = madvise_update_vma(vma, prev, start, end, new_flags,
+ vma_anon_name(vma));

out:
if (error == -ENOMEM)
@@ -494,6 +517,30 @@ int madvise_walk_vmas(unsigned long start, unsigned long end,
return unmapped_error;
}

+int madvise_set_anon_name(unsigned long start, unsigned long len_in,
+ unsigned long name_addr)
+{
+ unsigned long end;
+ unsigned long len;
+
+ if (start & ~PAGE_MASK)
+ return -EINVAL;
+ len = (len_in + ~PAGE_MASK) & PAGE_MASK;
+
+ /* Check to see whether len was rounded up from small -ve to zero */
+ if (len_in && !len)
+ return -EINVAL;
+
+ end = start + len;
+ if (end < start)
+ return -EINVAL;
+
+ if (end == start)
+ return 0;
+
+ return madvise_walk_vmas(start, end, name_addr, madvise_vma_anon_name);
+}
+
/*
* The madvise(2) system call.
*
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 04729647f359..ecc7bf226343 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -766,7 +766,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
((vmstart - vma->vm_start) >> PAGE_SHIFT);
prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
vma->anon_vma, vma->vm_file, pgoff,
- new_pol);
+ new_pol, vma_anon_name(vma));
if (prev) {
vma = prev;
next = vma->vm_next;
diff --git a/mm/mlock.c b/mm/mlock.c
index d480cd6fc475..7bb0d19f7cea 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -521,7 +521,8 @@ 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_anon_name(vma));
if (*prev) {
vma = *prev;
goto success;
diff --git a/mm/mmap.c b/mm/mmap.c
index 9d548512ff8a..09b899f1faf4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -893,7 +893,8 @@ 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)
{
if (vma->vm_flags ^ vm_flags)
return 0;
@@ -901,6 +902,8 @@ 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_anon_name(vma) != anon_name)
+ return 0;
return 1;
}

@@ -931,9 +934,10 @@ 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;
@@ -950,9 +954,10 @@ 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_pages(vma);
@@ -963,9 +968,9 @@ 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
@@ -995,7 +1000,8 @@ 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;
@@ -1021,15 +1027,15 @@ 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 */
@@ -1049,8 +1055,8 @@ 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);
@@ -1522,7 +1528,8 @@ 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;

@@ -2634,7 +2641,7 @@ static 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;

@@ -2792,7 +2799,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
return NULL; /* should never get here */
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_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 a3af058f68e4..36eaa694fdb7 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -274,7 +274,8 @@ 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_anon_name(vma));
if (*pprev) {
vma = *pprev;
goto success;
--
1.8.4.1


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