proc: revert /proc/<pid>/maps [stack:TID] annotation
Commit b76437579d13 ("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 combinations.
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.
Siddesh said:
"The end users needed a way to identify thread stacks programmatically and
there wasn't a way to do that. I'm afraid I no longer remember (or have
access to the resources that would aid my memory since I changed
employers) the details of their requirement. However, I did do this on my
own time because I thought it was an interesting project for me and nobody
really gave any feedback then as to its utility, so as far as I am
concerned you could roll back the main thread maps information since the
information is available in the thread-specific files"
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
Cc: Shaohua Li <shli@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index e0d64c9..faacb0c 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -123,23 +123,26 @@
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;
+ struct mm_struct *mm = vma->vm_mm;
+ int stack = 0;
- rcu_read_lock();
- task = pid_task(proc_pid(inode), PIDTYPE_PID);
- if (task) {
- task = task_of_stack(task, vma, is_pid);
+ 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 +184,9 @@
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');