Commit 2fdc8690 authored Aug 13, 2008 by Ingo Molnar

x86: add MAP_STACK mmap flag

as per this discussion:

   http://lkml.org/lkml/2008/8/12/423



Pardo reported that 64-bit threaded apps, if their stacks exceed the
combined size of ~4GB, slow down drastically in pthread_create() - because
glibc uses MAP_32BIT to allocate the stacks. The use of MAP_32BIT is
a legacy hack - to speed up context switching on certain early model
64-bit P4 CPUs.

So introduce a new flag to be used by glibc instead, to not constrain
64-bit apps like this.

glibc can switch to this new flag straight away - it will be ignored
by the kernel. If those old CPUs ever matter to anyone, support for
it can be implemented.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Ulrich Drepper <drepper@gmail.com>

parent 8d6ea967

include/asm-x86/mman.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -12,6 +12,7 @@
		#define MAP_NORESERVE 0x4000 /* don't check for reservations */
		#define MAP_POPULATE 0x8000 /* populate (prefault) pagetables */
		#define MAP_NONBLOCK 0x10000 /* do not block on IO */
		#define MAP_STACK 0x20000 /* give out an address that is best suited for process/thread stacks */

		#define MCL_CURRENT 1 /* lock all current mappings */
		#define MCL_FUTURE 2 /* lock all future mappings */