linux-kernel - Re: [PATCH 1/4] mm/page_alloc: fix non cma alloc context

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Message-ID: <CAAmzW4PPoSU6s8SQKRZAgLbfHz6LY5QXPWWjv2+iCM5iM3j51A@mail.gmail.com>
Date:   Fri, 17 Jul 2020 18:14:14 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-team@....com" <kernel-team@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        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>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/4] mm/page_alloc: fix non cma alloc context

2020년 7월 17일 (금) 오후 5:32, David Laight <David.Laight@...lab.com>님이 작성:
>
> From: js1304@...il.com
> > Sent: 15 July 2020 06:05
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > Currently, preventing cma area in page allocation is implemented by using
> > current_gfp_context(). However, there are two problems of this
> > implementation.
> ...
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6416d08..cd53894 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> ...
> > @@ -3693,6 +3691,16 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
> >       return alloc_flags;
> >  }
> >
> > +static inline void current_alloc_flags(gfp_t gfp_mask,
> > +                             unsigned int *alloc_flags)
> > +{
> > +     unsigned int pflags = READ_ONCE(current->flags);
> > +
> > +     if (!(pflags & PF_MEMALLOC_NOCMA) &&
> > +             gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> > +             *alloc_flags |= ALLOC_CMA;
> > +}
> > +
>
> I'd guess this would be easier to understand and probably generate
> better code if renamed and used as:
>         alloc_flags |= can_alloc_cma(gpf_mask);
>
> Given it is a 'static inline' the compiler might end up
> generating the same code.
> If you needed to clear a flag doing:
>         alloc_flags = current_alloc_flags(gpf_mask, alloc_flags);
> is much better for non-inlined function.

Vlastimil suggested this way and I have agreed with that. Anyway,
thanks for the suggestion.

Thanks.