linux-kernel - Re: [PATCH] mm, thp: relax __GFP_THISNODE for MADV

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Date:   Tue, 11 Sep 2018 10:51:12 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Stefan Priebe <s.priebe@...fihost.ag>
Subject: Re: [PATCH] mm, thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings

On 09/10/2018 10:08 PM, David Rientjes wrote:
> When Andrea brought this up, I suggested that the full solution would be a 
> MPOL_F_HUGEPAGE flag that could define thp allocation policy -- the added 

Can you elaborate on the semantics of this? You mean that a given vma
could now have two mempolicies, where one would be for hugepages only?
That's likely much more easy to suggest than to implement, with all uapi
consequences...

> benefit is that we could replace the thp "defrag" mode default by setting 
> this as part of default_policy.  Right now, MADV_HUGEPAGE users are 
> concerned about (1) getting thp when system-wide it is not default and (2) 
> additional fault latency when direct compaction is not default.  They are 
> not anticipating the degradation of remote access latency, so overloading 
> the meaning of the mode is probably not a good idea.
>