Re: + mm-oom-let-oom_reap_task-and-exit_mmap-to-run-concurrently.patch added to -mm tree

[Michal Hocko <mhocko@kernel.org>]

On Thu 17-08-17 19:12:40, Andrea Arcangeli wrote:
> On Wed, Aug 16, 2017 at 03:23:29PM +0200, Michal Hocko wrote:
> > Reviewed-by: Michal Hocko <mhocko@suse.com>
> 
> Thanks for the review!
> 
> There's this further possible microoptimization that can be folded on top.
> 
> >From 76bf017f923581d15fe01249af92b0d757752a9f Mon Sep 17 00:00:00 2001
> From: Andrea Arcangeli <aarcange@redhat.com>
> Date: Thu, 17 Aug 2017 18:39:46 +0200
> Subject: [PATCH 1/1] mm: oom: let oom_reap_task and exit_mmap run
>  concurrently, add unlikely
> 
> Microoptimization to fold before merging.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
>  mm/mmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 013170e5c8a4..ab0026a8acc4 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3003,7 +3003,7 @@ void exit_mmap(struct mm_struct *mm)
>  	unmap_vmas(&tlb, vma, 0, -1);
>  
>  	set_bit(MMF_OOM_SKIP, &mm->flags);
> -	if (tsk_is_oom_victim(current)) {
> +	if (unlikely(tsk_is_oom_victim(current))) {

I dunno. This doesn't make any difference in the generated code for
me (with gcc 6.4). If anything we might wan't to putt unlikely inside
tsk_is_oom_victim. Or even go further and use a jump label to get any
conditional paths out of way.

>  		/*
>  		 * Wait for oom_reap_task() to stop working on this
>  		 * mm. Because MMF_OOM_SKIP is already set before
> 

-- 
Michal Hocko
SUSE Labs

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