On venerd=EC 30 marzo 2007, Jeff Dike wrote:
quoted text
> flush_thread doesn't need to do a full page table walk in order to
> clear the address space.  It knows what the end result needs to be, so
> it can call unmap directly.
>
> This results in a 10-20% speedup in an exec from bash.

Oh, yeah!
When porting part of Ingo's work, I realized that a similar thing can be do=
ne=20
for fork().

If the whole address space is unmapped in init_new_context_skas(), the firs=
t=20
fix_range_common() call won't need to call unmap at all. He did this with=20
remap_file_pages(), where init_new_context_skas() must "unmap" everything=20
anyway.

This is giving some speedup in lmbench (5% better in fork proc, 2% better i=
n=20
exec proc), but the results are still controversial, there is one benchmark=
=20
with a 2% slowdown (called 'mmap latency').

In a loop, it maps, touches a byte per page and unmaps a region with growin=
g=20
size (up to 32MB).

However, since results aren't yet stable for some other benchmark (context=
=20
switching benchmark is crazy), I'm still studying on this.

quoted text
> Signed-off-by: Jeff Dike <jdike@linux.intel.com>
> --
>  arch/um/kernel/skas/exec.c |   12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.21-mm/arch/um/kernel/skas/exec.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
quoted text
> --- linux-2.6.21-mm.orig/arch/um/kernel/skas/exec.c	2007-03-30
> 10:28:24.000000000 -0400 +++
> linux-2.6.21-mm/arch/um/kernel/skas/exec.c	2007-03-30 10:30:15.000000000
> -0400 @@ -17,7 +17,17 @@
>
>  void flush_thread_skas(void)
>  {
> -	force_flush_all();
> +	void *data =3D NULL;
> +	unsigned long end =3D proc_mm ? task_size : CONFIG_STUB_START;
> +	int ret;
> +
> +	ret =3D unmap(&current->mm->context.skas.id, 0, end, 1, &data);
> +	if(ret){
> +		printk("flush_thread_skas - clearing address space failed, "
> +		       "err =3D %d\n", ret);
> +		force_sig(SIGKILL, current);
> +	}
> +
>  	switch_mm_skas(&current->mm->context.skas.id);
>  }


=2D-=20
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade