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Commit 65376df5 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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proc: revert /proc/<pid>/maps [stack:TID] annotation 



Commit b7643757 ("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: default avatarJohannes 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5c2ff95e

Documentation/filesystems/proc.txt

+3 −6
Original line number Diff line number Diff line
@@ -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

fs/proc/task_mmu.c

+23 −43
Original line number Diff line number Diff line
@@ -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)

{

	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;

	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);

		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();



	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)) {

		if (is_stack(priv, vma, is_pid))

			name = "[stack]";

			} else {

				/* Thread stack in /proc/PID/maps */

				seq_pad(m, ' ');

				seq_printf(m, "[stack:%d]", tid);

			}

		}

	}



done:
@@ -1618,19 +1609,8 @@ 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))

	} else if (is_stack(proc_priv, vma, is_pid)) {

		seq_puts(m, " stack");

			else

				seq_printf(m, " stack:%d", tid);

		}

	}



	if (is_vm_hugetlb_page(vma))

fs/proc/task_nommu.c

+20 −29
Original line number Diff line number Diff line
@@ -123,23 +123,26 @@ 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 mm_struct *mm = vma->vm_mm;

	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;

	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);

		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();



	return ret;

	}

	return stack;

}



/*
@@ -181,21 +184,9 @@ 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) {

	} else if (mm && is_stack(priv, vma, is_pid)) {

		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);

		}

	}



	seq_putc(m, '\n');

include/linux/mm.h

+1 −2
Original line number Diff line number Diff line
@@ -1341,8 +1341,7 @@ 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,

mm/util.c

+1 −26
Original line number Diff line number Diff line
@@ -230,36 +230,11 @@ 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)

{