Re: [PATCHv2] Add per-process flag to control thp

[Rik van Riel]

On 08/03/2013 01:01 PM, Oleg Nesterov wrote:

> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +	p->thp_disabled = current->thp_disabled;
> > +#endif
>
> Unneeded. It will be copied by dup_task_struct() automagically.
>
> But I simply can't understand why this flag is per-thread. It should be
> mm flag, no?

It has to be per-mm for another reason, too.

Think about what were to happen if one process were ptracing
a process with the thp_disabled flag, and ended up causing a
new anonymous page to be faulted in.

With the thp_disabled flag in the task, get_user_pages would
end up not seeing the flag, and the task could get a transparent
huge page.

With the thp_disabled flag in the mm, it would be possible for
get_user_pages to easily find the flag, and do the right thing.

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