linux-kernel - Re: [PATCH v4 06/11] mm/migrate: make a standard migration target allocation function

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Date:   Tue, 7 Jul 2020 16:49:51 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 06/11] mm/migrate: make a standard migration target
 allocation function

On 7/7/20 9:44 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> There are some similar functions for migration target allocation.  Since
> there is no fundamental difference, it's better to keep just one rather
> than keeping all variants.  This patch implements base migration target
> allocation function.  In the following patches, variants will be converted
> to use this function.
> 
> Changes should be mechanical but there are some differences. First, Some
> callers' nodemask is assgined to NULL since NULL nodemask will be
> considered as all available nodes, that is, &node_states[N_MEMORY].
> Second, for hugetlb page allocation, gfp_mask is ORed since a user could
> provide a gfp_mask from now on.

I think that's wrong. See how htlb_alloc_mask() determines between
GFP_HIGHUSER_MOVABLE and GFP_HIGHUSER, but then you OR it with __GFP_MOVABLE so
it's always GFP_HIGHUSER_MOVABLE.
Yeah, gfp_mask for hugeltb become exposed in new_page_nodemask() after v4 3/11
patch, but that doesn't mean we can start modifying it :/