Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

[Jerome Glisse]

On Fri, Aug 24, 2018 at 06:40:03PM +0200, Michal Hocko wrote:
> On Fri 24-08-18 11:12:40, Jerome Glisse wrote:
> [...]
> > I am fine with Michal patch, i already said so couple month ago first time
> > this discussion did pop up, Michal you can add:
> > 
> > Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> 
> So I guess the below is the patch you were talking about?
> 
> From f7ac75277d526dccd011f343818dc6af627af2af Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Fri, 24 Aug 2018 15:32:24 +0200
> Subject: [PATCH] mm, mmu_notifier: be explicit about range invalition
>  non-blocking mode
> 
> If invalidate_range_start is called for !blocking mode then all
> callbacks have to guarantee they will no block/sleep. The same obviously
> applies to invalidate_range_end because this operation pairs with the
> former and they are called from the same context. Make sure this is
> appropriately documented.

In my branch i already updated HMM to be like other existing user
ie all blocking operation in the start callback. But yes it would
be wise to added such comments.


> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  include/linux/mmu_notifier.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index 133ba78820ee..698e371aafe3 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -153,7 +153,9 @@ struct mmu_notifier_ops {
>  	 *
>  	 * If blockable argument is set to false then the callback cannot
>  	 * sleep and has to return with -EAGAIN. 0 should be returned
> -	 * otherwise.
> +	 * otherwise. Please note that if invalidate_range_start approves
> +	 * a non-blocking behavior then the same applies to
> +	 * invalidate_range_end.
>  	 *
>  	 */
>  	int (*invalidate_range_start)(struct mmu_notifier *mn,
> -- 
> 2.18.0
> 
> -- 
> Michal Hocko
> SUSE Labs