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

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Message-ID: <CAAmzW4MLc8bmkYW1q1fL_WRFQHksX-oy9tS-s9Kb-A=ZEeGETQ@mail.gmail.com>
Date:   Fri, 17 Jul 2020 16:29:17 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     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>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/4] mm/page_alloc: fix non cma alloc context

2020년 7월 16일 (목) 오후 4:45, Vlastimil Babka <vbabka@...e.cz>님이 작성:
>
> On 7/16/20 9:27 AM, Joonsoo Kim wrote:
> > 2020년 7월 15일 (수) 오후 5:24, Vlastimil Babka <vbabka@...e.cz>님이 작성:
> >> >  /*
> >> >   * get_page_from_freelist goes through the zonelist trying to allocate
> >> >   * a page.
> >> > @@ -3706,6 +3714,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> >> >       struct pglist_data *last_pgdat_dirty_limit = NULL;
> >> >       bool no_fallback;
> >> >
> >> > +     current_alloc_flags(gfp_mask, &alloc_flags);
> >>
> >> I don't see why to move the test here? It will still be executed in the
> >> fastpath, if that's what you wanted to avoid.
> >
> > I want to execute it on the fastpath, too. Reason that I moved it here
> > is that alloc_flags could be reset on slowpath. See the code where
> > __gfp_pfmemalloc_flags() is on. This is the only place that I can apply
> > this option to all the allocation paths at once.
>
> But get_page_from_freelist() might be called multiple times in the slowpath, and
> also anyone looking for gfp and alloc flags setup will likely not examine this
> function. I don't see a problem in having it in two places that already deal
> with alloc_flags setup, as it is now.

I agree that anyone looking alloc flags will miss that function easily. Okay.
I will place it on its original place, although we now need to add one
more place.
*Three places* are gfp_to_alloc_flags(), prepare_alloc_pages() and
__gfp_pfmemalloc_flags().

Thanks.