linux-kernel - Re: [QUESTIONS] THP allocation in NUMA fault migration path

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Date:   Thu, 18 Apr 2019 08:32:18 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [QUESTIONS] THP allocation in NUMA fault migration path

On Wed 17-04-19 21:15:41, Yang Shi wrote:
> Hi folks,
> 
> 
> I noticed that there might be new THP allocation in NUMA fault migration
> path (migrate_misplaced_transhuge_page()) even when THP is disabled (set to
> "never"). When THP is set to "never", there should be not any new THP
> allocation, but the migration path is kind of special. So I'm not quite sure
> if this is the expected behavior or not?
> 
> 
> And, it looks this allocation disregards defrag setting too, is this
> expected behavior too?H

Could you point to the specific code? But in general the miTgration path
should allocate the memory matching the migration origin. If the origin
was a THP then I find it quite natural if the target was a huge page as
well. How hard the allocation should try is another question and I
suspect we do want to obedy the defrag setting.
-- 
Michal Hocko
SUSE Labs