Gitweb:     http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=cd98a0...
Commit:     cd98a04a59e2f94fa64d5bf1e26498d27427d5e7
Parent:     45edb89ffd6386f95a7a9e1e5461b0e61c76aa14
Author:     Ingo Molnar <mingo@elte.hu>
AuthorDate: Wed Aug 13 18:02:18 2008 +0200
Committer:  Linus Torvalds <torvalds@linux-foundation.org>
CommitDate: Fri Aug 15 11:45:19 2008 -0700

    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>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/asm-x86/mman.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/asm-x86/mman.h b/include/asm-x86/mman.h
index c1682b5..90bc410 100644
--- a/include/asm-x86/mman.h
+++ b/include/asm-x86/mman.h
@@ -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 */
--

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