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/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..0b50d78 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1341,8 +1341,7 @@
!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,