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Date: Tue, 19 Jan 2016 13:02:39 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Shaohua Li <shli@...com>,
Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-team@...com
Subject: [PATCH] proc: revert /proc/<pid>/maps [stack:TID] annotation
b764375 ("procfs: mark thread stack correctly in proc/<pid>/maps")
added [stack:TID] annotation to /proc/<pid>/maps. Finding the task of
a stack VMA requires walking the entire thread list, turning this into
quadratic behavior: a thousand threads means a thousand stacks, so the
rendering of /proc/<pid>/maps needs to look at a million threads. The
cost is not in proportion to the usefulness as described in the patch.
Drop the [stack:TID] annotation to make /proc/<pid>/maps (and
/proc/<pid>/numa_maps) usable again for higher thread counts.
The [stack] annotation inside /proc/<pid>/task/<tid>/maps is retained,
as identifying the stack VMA there is an O(1) operation.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
Documentation/filesystems/proc.txt | 9 ++----
fs/proc/task_mmu.c | 66 +++++++++++++-------------------------
fs/proc/task_nommu.c | 48 +++++++++++----------------
include/linux/mm.h | 3 +-
mm/util.c | 27 +---------------
5 files changed, 47 insertions(+), 106 deletions(-)
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index e95aa1c..4e95796 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -356,7 +356,7 @@ address perms offset dev inode pathname
a7cb1000-a7cb2000 ---p 00000000 00:00 0
a7cb2000-a7eb2000 rw-p 00000000 00:00 0
a7eb2000-a7eb3000 ---p 00000000 00:00 0
-a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack:1001]
+a7eb3000-a7ed5000 rw-p 00000000 00:00 0
a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
@@ -388,7 +388,6 @@ is not associated with a file:
[heap] = the heap of the program
[stack] = the stack of the main process
- [stack:1001] = the stack of the thread with tid 1001
[vdso] = the "virtual dynamic shared object",
the kernel system call handler
@@ -396,10 +395,8 @@ is not associated with a file:
The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
of the individual tasks of a process. In this file you will see a mapping marked
-as [stack] if that task sees it as a stack. This is a key difference from the
-content of /proc/PID/maps, where you will see all mappings that are being used
-as stack by all of those tasks. Hence, for the example above, the task-level
-map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
+as [stack] if that task sees it as a stack. Hence, for the example above, the
+task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 65a1b6c..81aa553 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -259,23 +259,29 @@ static int do_maps_open(struct inode *inode, struct file *file,
sizeof(struct proc_maps_private));
}
-static pid_t pid_of_stack(struct proc_maps_private *priv,
- struct vm_area_struct *vma, bool is_pid)
+/*
+ * Indicate if the VMA is a stack for the given task; for
+ * /proc/PID/maps that is the stack of the main task.
+ */
+static int is_stack(struct proc_maps_private *priv,
+ struct vm_area_struct *vma, int is_pid)
{
- struct inode *inode = priv->inode;
- struct task_struct *task;
- pid_t ret = 0;
+ int stack = 0;
+
+ if (is_pid) {
+ stack = vma->vm_start <= vma->vm_mm->start_stack &&
+ vma->vm_end >= vma->vm_mm->start_stack;
+ } else {
+ struct inode *inode = priv->inode;
+ struct task_struct *task;
- rcu_read_lock();
- task = pid_task(proc_pid(inode), PIDTYPE_PID);
- if (task) {
- task = task_of_stack(task, vma, is_pid);
+ rcu_read_lock();
+ task = pid_task(proc_pid(inode), PIDTYPE_PID);
if (task)
- ret = task_pid_nr_ns(task, inode->i_sb->s_fs_info);
+ stack = vma_is_stack_for_task(vma, task);
+ rcu_read_unlock();
}
- rcu_read_unlock();
-
- return ret;
+ return stack;
}
static void
@@ -335,8 +341,6 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
name = arch_vma_name(vma);
if (!name) {
- pid_t tid;
-
if (!mm) {
name = "[vdso]";
goto done;
@@ -348,21 +352,8 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
goto done;
}
- tid = pid_of_stack(priv, vma, is_pid);
- if (tid != 0) {
- /*
- * Thread stack in /proc/PID/task/TID/maps or
- * the main process stack.
- */
- if (!is_pid || (vma->vm_start <= mm->start_stack &&
- vma->vm_end >= mm->start_stack)) {
- name = "[stack]";
- } else {
- /* Thread stack in /proc/PID/maps */
- seq_pad(m, ' ');
- seq_printf(m, "[stack:%d]", tid);
- }
- }
+ if (is_stack(priv, vma, is_pid))
+ name = "[stack]";
}
done:
@@ -1613,19 +1604,8 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
seq_file_path(m, file, "\n\t= ");
} else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) {
seq_puts(m, " heap");
- } else {
- pid_t tid = pid_of_stack(proc_priv, vma, is_pid);
- if (tid != 0) {
- /*
- * Thread stack in /proc/PID/task/TID/maps or
- * the main process stack.
- */
- if (!is_pid || (vma->vm_start <= mm->start_stack &&
- vma->vm_end >= mm->start_stack))
- seq_puts(m, " stack");
- else
- seq_printf(m, " stack:%d", tid);
- }
+ } else if (is_stack(proc_priv, vma, is_pid)) {
+ seq_puts(m, " stack");
}
if (is_vm_hugetlb_page(vma))
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index e0d64c9..60ab72e 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -123,23 +123,25 @@ unsigned long task_statm(struct mm_struct *mm,
return size;
}
-static pid_t pid_of_stack(struct proc_maps_private *priv,
- struct vm_area_struct *vma, bool is_pid)
+static int is_stack(struct proc_maps_private *priv,
+ struct vm_area_struct *vma, int is_pid)
{
- struct inode *inode = priv->inode;
- struct task_struct *task;
- pid_t ret = 0;
-
- rcu_read_lock();
- task = pid_task(proc_pid(inode), PIDTYPE_PID);
- if (task) {
- task = task_of_stack(task, vma, is_pid);
+ int stack = 0;
+
+ if (is_pid) {
+ stack = vma->vm_start <= mm->start_stack &&
+ vma->vm_end >= mm->start_stack;
+ } else {
+ struct inode *inode = priv->inode;
+ struct task_struct *task;
+
+ rcu_read_lock();
+ task = pid_task(proc_pid(inode), PIDTYPE_PID);
if (task)
- ret = task_pid_nr_ns(task, inode->i_sb->s_fs_info);
+ stack = vma_is_stack_for_task(vma, task);
+ rcu_read_unlock();
}
- rcu_read_unlock();
-
- return ret;
+ return stack;
}
/*
@@ -181,21 +183,9 @@ static int nommu_vma_show(struct seq_file *m, struct vm_area_struct *vma,
if (file) {
seq_pad(m, ' ');
seq_file_path(m, file, "");
- } else if (mm) {
- pid_t tid = pid_of_stack(priv, vma, is_pid);
-
- if (tid != 0) {
- seq_pad(m, ' ');
- /*
- * Thread stack in /proc/PID/task/TID/maps or
- * the main process stack.
- */
- if (!is_pid || (vma->vm_start <= mm->start_stack &&
- vma->vm_end >= mm->start_stack))
- seq_printf(m, "[stack]");
- else
- seq_printf(m, "[stack:%d]", tid);
- }
+ } else if (mm && is_stack(priv, vma, is_pid)) {
+ seq_pad(m, ' ');
+ seq_printf(m, "[stack]");
}
seq_putc(m, '\n');
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7286d5b..0cbed33 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1343,8 +1343,7 @@ static inline int stack_guard_page_end(struct vm_area_struct *vma,
!vma_growsup(vma->vm_next, addr);
}
-extern struct task_struct *task_of_stack(struct task_struct *task,
- struct vm_area_struct *vma, bool in_group);
+int vma_is_stack_for_task(struct vm_area_struct *vma, struct task_struct *t);
extern unsigned long move_page_tables(struct vm_area_struct *vma,
unsigned long old_addr, struct vm_area_struct *new_vma,
diff --git a/mm/util.c b/mm/util.c
index bafd4c5..4f841e5 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -260,36 +260,11 @@ void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
}
/* Check if the vma is being used as a stack by this task */
-static int vm_is_stack_for_task(struct task_struct *t,
- struct vm_area_struct *vma)
+int vma_is_stack_for_task(struct vm_area_struct *vma, struct task_struct *t)
{
return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t));
}
-/*
- * Check if the vma is being used as a stack.
- * If is_group is non-zero, check in the entire thread group or else
- * just check in the current task. Returns the task_struct of the task
- * that the vma is stack for. Must be called under rcu_read_lock().
- */
-struct task_struct *task_of_stack(struct task_struct *task,
- struct vm_area_struct *vma, bool in_group)
-{
- if (vm_is_stack_for_task(task, vma))
- return task;
-
- if (in_group) {
- struct task_struct *t;
-
- for_each_thread(task, t) {
- if (vm_is_stack_for_task(t, vma))
- return t;
- }
- }
-
- return NULL;
-}
-
#if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
void arch_pick_mmap_layout(struct mm_struct *mm)
{
--
2.7.0
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