linux-kernel - Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

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Message-ID: <52ec4899-80df-4cbe-41f1-e0a29e838afa@redhat.com>
Date:   Tue, 12 Jan 2021 15:41:02 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Muchun Song <songmuchun@...edance.com>, mike.kravetz@...cle.com,
        akpm@...ux-foundation.org, n-horiguchi@...jp.nec.com,
        ak@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose
 refcount is one

On 12.01.21 15:23, Michal Hocko wrote:
> On Tue 12-01-21 13:16:45, Michal Hocko wrote:
> [...]
>> Well, currently pool pages are not migrateable but you are right that
>> this is likely something that we will need to look into in the future
>> and this optimization would stand in the way.
> 
> After some more thinking I believe I was wrong in my last statement.
> This optimization shouldn't have any effect on pages on the pool as
> those stay at reference count 0 and they cannot be isolated either
> (clear_page_huge_active before it is enqueued).
> 
> That being said, the migration code would still have to learn about
> about this pages but that is out of scope of this discussion.
> 
> Sorry about the confusion from my side.
> 

At this point I am fairly confused what's working at what's not :D

I think this will require more thought, on how to teach
alloc_contig_range() (and eventually in some cases offline_pages()?) to
do the right thing.

-- 
Thanks,

David / dhildenb