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

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Date:   Thu, 27 Jul 2017 07:52:08 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: gigantic hugepages vs. movable zones

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. That may conflict with CMA pages ? Wondering whether
we should check for page's pageblock migrate type in
pfn_range_valid_gigantic() ?

-aneesh