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

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Date:   Thu, 27 Jul 2017 13:30:31 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Luiz Capitulino <lcapitulino@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: gigantic hugepages vs. movable zones



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 ?

-aneesh