Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

[Muchun Song]

On Tue, Feb 16, 2021 at 4:15 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Tue 16-02-21 12:34:41, Muchun Song wrote:
> > On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> [...]
> > > > Using GFP_KERNEL will also use the current task cpuset to allocate
> > > > memory. Do we have an interface to ignore current task cpuset？If not,
> > > > WQ may be the only option and it also will not limit the context of
> > > > put_page. Right?
> > >
> > > Well, GFP_KERNEL is constrained to the task cpuset only if the said
> > > cpuset is hardwalled IIRC. But I do not see why this is a problem.
> >
> > I mean that if there are more than one node in the system,
> > but the current task cpuset only allows one node.
>
> How would that cpuset get a huge pages from a node which is not part of
> the cpuset? Well, that would be possible if the cpuset was dynamic but I
> am not sure that such a configuration would be very sensible along with
> hardwall setup.

Got it. I didn't realize this before. Thanks.

>
> > If current
> > node has no memory and other nodes have enough memory.
> > We can fail to allocate vmemmap pages. But actually it is
> > suitable to allocate vmemmap pages from other nodes.
> > Right?
>
> Falling back to a different node would be very suboptimal because then
> you would have vmemmap back by remote pages. We do not want that.
> --
> Michal Hocko
> SUSE Labs