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

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