On Fri, Feb 3, 2012 at 3:10 AM, KOSAKI Motohiro
[off-list ref] wrote:

quoted

 extern unsigned long move_page_tables(struct vm_area_struct *vma,

diff --git a/mm/mmap.c b/mm/mmap.c
index 3f758c7..2f9f540 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -992,6 +992,9 @@ unsigned long do_mmap_pgoff(struct file *file,

unsigned long addr,
       vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
                       mm->def_flags | VM_MAYREAD | VM_MAYWRITE |
VM_MAYEXEC;

+       if (flags&  MAP_STACK)
+               vm_flags |= VM_STACK_FLAGS;

??
MAP_STACK doesn't mean auto stack expansion. Why do you turn on
VM_GROWSDOWN?
Seems incorrect.

Right now MAP_STACK does not mean anything since it is ignored. The
intention of this behaviour change is to make MAP_STACK mean that the
map is going to be used as a stack and hence, set it up like a stack
ought to be. I could not really think of a valid case for fixed size
stacks; it looks like a limitation in the pthread implementation in
glibc rather than a feature. So this patch will actually result in
uniform behaviour across threads when it comes to stacks.

This does change vm accounting since thread stacks were earlier
accounted as anon memory.

-- 
Siddhesh Poyarekar
http://siddhesh.in

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