linux-kernel - Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration

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Message-ID: <20181009141442.GT8528@dhcp22.suse.cz>
Date:   Tue, 9 Oct 2018 16:14:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, suzuki.poulose@....com,
        punit.agrawal@....com, will.deacon@....com, Steven.Price@....com,
        catalin.marinas@....com, mike.kravetz@...cle.com,
        n-horiguchi@...jp.nec.com
Subject: Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration

On Fri 05-10-18 13:04:43, Anshuman Khandual wrote:
> Does the following sound close enough to what you are looking for ?

I do not think so

> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 9df1d59..070c419 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -504,6 +504,13 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>         return arch_hugetlb_migration_supported(h);
>  }
>  
> +static inline bool hugepage_movable_required(struct hstate *h)
> +{
> +       if (hstate_is_gigantic(h))
> +               return true;
> +       return false;
> +}
> +

Apart from naming (hugepage_movable_supported?) the above doesn't do the
most essential thing to query whether the hugepage migration is
supported at all. Apart from that i would expect the logic to be revers.
We do not really support giga pages migration enough to support them in
movable zone.
> @@ -1652,6 +1655,9 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
>  {
>         gfp_t gfp_mask = htlb_alloc_mask(h);
>  
> +       if (hugepage_movable_required(h))
> +               gfp_mask |= __GFP_MOVABLE;
> +

And besides that this really want to live in htlb_alloc_mask because
this is really an allocation policy. It would be unmap_and_move_huge_page
to call hugepage_migration_supported. The later is the one to allow for
an arch specific override.

Makes sense?
-- 
Michal Hocko
SUSE Labs