linux-kernel - Re: [PATCH v3 3/8] mm/hugetlb: unify migration callbacks

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Date:   Fri, 3 Jul 2020 09:55:33 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <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>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 3/8] mm/hugetlb: unify migration callbacks

2020년 7월 3일 (금) 오전 1:13, Vlastimil Babka <vbabka@...e.cz>님이 작성:
>
> On 6/26/20 6:02 AM, Joonsoo Kim wrote:
> > 2020년 6월 25일 (목) 오후 8:26, Michal Hocko <mhocko@...nel.org>님이 작성:
> >>
> >> On Tue 23-06-20 15:13:43, Joonsoo Kim wrote:
> >> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >> >
> >> > There is no difference between two migration callback functions,
> >> > alloc_huge_page_node() and alloc_huge_page_nodemask(), except
> >> > __GFP_THISNODE handling. This patch adds an argument, gfp_mask, on
> >> > alloc_huge_page_nodemask() and replace the callsite for
> >> > alloc_huge_page_node() with the call to
> >> > alloc_huge_page_nodemask(..., __GFP_THISNODE).
> >> >
> >> > It's safe to remove a node id check in alloc_huge_page_node() since
> >> > there is no caller passing NUMA_NO_NODE as a node id.
> >>
> >> Yes this is indeed safe. alloc_huge_page_node used to be called from
> >> other internal hugetlb allocation layer and that allowed NUMA_NO_NODE as
> >> well. Now it is called only from the mempolicy migration callback and
> >> that always specifies a node and want to stick with that node.
> >>
> >> But I have to say I really dislike the gfp semantic because it is
> >> different from any other allocation function I can think of. It
> >> specifies what to be added rather than what should be used.
> >>
> >> Removing the function is ok but please use the full gfp mask instead
> >> or if that is impractical for some reason (wich shouldn't be the case
> >> as htlb_alloc_mask should be trivial to make static inline) make it
> >> explicit that this is not a gfp_mask but a gfp modifier and explicitly
> >> state which modifiers are allowed.
> >
> > Okay. I will try to solve your concern. Concrete solution is not yet prepared
> > but perhaps I will use full gfp_mask by using htlb_alloc_mask() in caller sites.
>
> Yeah, that should be feasible. alloc_huge_page_vma() already does
> htlb_alloc_mask(h). In alloc_new_node_page() and new_page_nodemask() it would be
> consistent with the other cases handled there (THP and base).

Okay. Will check it.

Thanks.