linux-kernel - Re: gigantic hugepages vs. movable zones

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Date:   Thu, 27 Jul 2017 10:22:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     Luiz Capitulino <lcapitulino@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: gigantic hugepages vs. movable zones

[CC for real]

On Thu 27-07-17 10:12:36, Michal Hocko wrote:
> On Thu 27-07-17 13:30:31, Aneesh Kumar K.V wrote:
> > 
> > 
> > On 07/27/2017 12:58 PM, Michal Hocko wrote:
> > >On Thu 27-07-17 07:52:08, Aneesh Kumar K.V wrote:
> > >>Michal Hocko <mhocko@...nel.org> writes:
> > >>
> > >>>Hi,
> > >>>I've just noticed that alloc_gigantic_page ignores movability of the
> > >>>gigantic page and it uses any existing zone. Considering that
> > >>>hugepage_migration_supported only supports 2MB and pgd level hugepages
> > >>>then 1GB pages are not migratable and as such allocating them from a
> > >>>movable zone will break the basic expectation of this zone. Standard
> > >>>hugetlb allocations try to avoid that by using htlb_alloc_mask and I
> > >>>believe we should do the same for gigantic pages as well.
> > >>>
> > >>>I suspect this behavior is not intentional. What do you think about the
> > >>>following untested patch?
> > >>
> > >>
> > >>I also noticed an unrelated issue with the usage of
> > >>start_isolate_page_range. On error we set the migrate type to
> > >>MIGRATE_MOVABLE.
> > >
> > >Why that should be a problem? I think it is perfectly OK to have
> > >MIGRATE_MOVABLE pageblocks inside kernel zones.
> > >
> > 
> > we can pick pages with migrate type movable and if we fail to isolate won't
> > we set the migrate type of that pages to MOVABLE ?
> 
> I do not see an immediate problem. GFP_KERNEL allocations can fallback
> to movable migrate pageblocks AFAIR. But I am not very much familiar
> with migratetypes. Vlastimil, could you have a look please?

-- 
Michal Hocko
SUSE Labs