linux-kernel - Re: [PATCH] mm/madvise: enable soft offline of HugeTLB pages at PUD level

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Message-ID: <20170929135554.6cz7lpjn7gepmlf4@node.shutemov.name>
Date:   Fri, 29 Sep 2017 16:55:54 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Alexandru Moise <00moses.alexander00@...il.com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com,
        aneesh.kumar@...ux.vnet.ibm.com, n-horiguchi@...jp.nec.com,
        mike.kravetz@...cle.com, khandual@...ux.vnet.ibm.com,
        punit.agrawal@....com, gerald.schaefer@...ibm.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/madvise: enable soft offline of HugeTLB pages at PUD
 level

On Wed, Sep 13, 2017 at 12:10:47PM +0200, Alexandru Moise wrote:
> since 94310cb we've been able to soft offline 1G hugepages at the PGD
> level, however x86_64 gigantic hugepages are at the PUD level so we
> should add an extra check to account for hstate order at PUD level.

Have you tested other cases affected by the change? It allows migration of
1G pages in general, which might be problematic.

It also makes these pages allocated with GFP_HIGHUSER_MOVABLE instead of
GFP_HIGHUSER. Any side effects there we should consider?

> I'm not sure if this also applies to 5 level page tables on x86_64
> however. Tested with 4 level pagetable.

There's nothing changed in this regard in 5-level paging mode. PUD is
still one gig and there are no new page sizes.

-- 
 Kirill A. Shutemov