Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <1595468942-29687-1-git-send-email-iamjoonsoo.kim@lge.com>
 <20200723180814.acde28b92ce6adc785a79120@linux-foundation.org>
 <CAAmzW4N9Y4W7CHenWA=TYu9tttgpYR=ZN+ky1vmXPgUJcjitAw@mail.gmail.com> <20200723193600.28e3eedd00925b22f7ca9780@linux-foundation.org>
In-Reply-To: <20200723193600.28e3eedd00925b22f7ca9780@linux-foundation.org>
From:   Joonsoo Kim <js1304@gmail.com>
Date:   Fri, 24 Jul 2020 12:04:02 +0900
Message-ID: <CAAmzW4NhY0iaE02vwf+2O+aeK66CoKG_-BvsgqpfwZv3Q-w8dA@mail.gmail.com>
Subject: Re: [PATCH v2] mm/page_alloc: fix memalloc_nocma_{save/restore} APIs
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, kernel-team@lge.com,
        Vlastimil Babka <vbabka@suse.cz>,
        Christoph Hellwig <hch@infradead.org>,
        Roman Gushchin <guro@fb.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Michal Hocko <mhocko@suse.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

2020=EB=85=84 7=EC=9B=94 24=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 11:36, =
Andrew Morton <akpm@linux-foundation.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=
=B1:
>
> On Fri, 24 Jul 2020 11:23:52 +0900 Joonsoo Kim <js1304@gmail.com> wrote:
>
> > > > Second, clearing __GFP_MOVABLE in current_gfp_context() has a side =
effect
> > > > to exclude the memory on the ZONE_MOVABLE for allocation target.
> > >
> > > More whoops.
> > >
> > > Could we please have a description of the end-user-visible effects of
> > > this change?  Very much needed when proposing a -stable backport, I t=
hink.
> >
> > In fact, there is no noticeable end-user-visible effect since the fallb=
ack would
> > cover the problematic case. It's mentioned in the commit description. P=
erhap,
> > performance would be improved due to reduced retry and more available m=
emory
> > (we can use ZONE_MOVABLE with this patch) but it would be neglectable.
> >
> > > d7fefcc8de9147c is over a year old.  Why did we only just discover
> > > this?  This makes one wonder how serious those end-user-visible effec=
ts
> > > are?
> >
> > As mentioned above, there is no visible problem to the end-user.
>
> OK, thanks.  In that case, I don't believe that a stable backport is
> appropriate?
>
> (Documentation/process/stable-kernel-rules.rst)

Thanks for the pointer!

Hmm... I'm not sure the correct way to handle this patch. I thought that
memalloc_nocma_{save,restore} is an API that is callable from the module.
If it is true, it's better to regard this patch as the stable candidate sin=
ce
out-of-tree modules could use it without the fallback and it would cause
a problem. But, yes, there is no visible problem to the end-user, at least,
within the mainline so it is possibly not a stable candidate.

Please share your opinion about this situation.

Thanks.