linux-kernel - Re: [RFC PATCH] mm,memory_hotplug: Unlock 1GB-hugetlb on x86

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Date:   Thu, 28 Feb 2019 15:08:17 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, david@...hat.com,
        mike.kravetz@...cle.com
Subject: Re: [RFC PATCH] mm,memory_hotplug: Unlock 1GB-hugetlb on x86_64

On Thu 28-02-19 14:40:54, Oscar Salvador wrote:
> On Thu, Feb 28, 2019 at 01:11:15PM +0100, Michal Hocko wrote:
> > On Thu 28-02-19 11:19:52, Oscar Salvador wrote:
> > > On Thu, Feb 28, 2019 at 10:55:35AM +0100, Michal Hocko wrote:
> > > > You seemed to miss my point or I am wrong here. If scan_movable_pages
> > > > skips over a hugetlb page then there is nothing to migrate it and it
> > > > will stay in the pfn range and the range will not become idle.
> > > 
> > > I might be misunterstanding you, but I am not sure I get you.
> > > 
> > > scan_movable_pages() can either skip or not a hugetlb page.
> > > In case it does, pfn will be incremented to skip the whole hugetlb
> > > range.
> > > If that happens, pfn will hold the next non-hugetlb page.
> > 
> > And as a result the previous hugetlb page doesn't get migrated right?
> > What does that mean? Well, the page is still in use and we cannot
> > proceed with offlining because the full range is not isolated right?
> 
> I might be clumsy today but I still fail to see the point of concern here.

No, it's me who is daft. I have misread the patch and seen that also
page_huge_active got removed. Now it makes perfect sense to me because
active pages are still handled properly.

I will leave the decision whether to split up the patch to you.

Acked-by: Michal Hocko <mhocko@...e.com>

and sorry for being dense here.

-- 
Michal Hocko
SUSE Labs