Re: [PATCH v7 7/7] mm/madvise: allow KSM hints for remote API

[Michal Hocko]

On Mon 09-03-20 14:11:17, Oleksandr Natalenko wrote:
> On Fri, Mar 06, 2020 at 05:08:18PM +0100, Vlastimil Babka wrote:
[...]
> > Dunno, it's nice to react to signals quickly, for any proces that gets them, no?
> 
> So, do you mean something like this?
> 
> ===
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 363ec8189561..b39c237cfcf4 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -849,7 +849,8 @@ static int unmerge_ksm_pages(struct vm_area_struct *vma,
>  	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
>  		if (ksm_test_exit(vma->vm_mm))
>  			break;
> -		if (signal_pending(current))
> +		if (signal_pending(current) ||
> +		    signal_pending(rcu_dereference(vma->vm_mm->owner)))
>  			err = -ERESTARTSYS;
>  		else
>  			err = break_ksm(vma, addr);
> ===

This is broken because mm might be attached to different tasks.
AFAIU this check is meant to allow quick backoff of the _calling_
process so that it doesn't waste time when the context is killed
already. I do not understand why should we care about any other context
here? What is the actual problem this would solve?

-- 
Michal Hocko
SUSE Labs