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Date:   Tue, 16 Feb 2021 09:15:51 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
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Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap
 pages associated with each HugeTLB page
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On Tue 16-02-21 12:34:41, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@suse.com> 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.

> 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