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;
Date:   Wed, 8 Jul 2020 13:32:54 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc:     Vlastimil Babka <vbabka@suse.cz>, Joonsoo Kim <js1304@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@lge.com,
        Christoph Hellwig <hch@infradead.org>,
        Roman Gushchin <guro@fb.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback CMA
 aware
Message-ID: <20200708113254.GI7271@dhcp22.suse.cz>
References: <1594107889-32228-1-git-send-email-iamjoonsoo.kim@lge.com>
 <1594107889-32228-5-git-send-email-iamjoonsoo.kim@lge.com>
 <c1cd6e11-08c3-5654-60e7-dec2eb80987a@suse.cz>
 <20200708071602.GB16543@js1304-desktop>
 <20200708074103.GD7271@dhcp22.suse.cz>
 <8549326e-7485-dd6d-1fa1-a899228b9b2f@suse.cz>
 <87h7uil1f7.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87h7uil1f7.fsf@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed 08-07-20 16:27:16, Aneesh Kumar K.V wrote:
> Vlastimil Babka <vbabka@suse.cz> writes:
> 
> > On 7/8/20 9:41 AM, Michal Hocko wrote:
> >> On Wed 08-07-20 16:16:02, Joonsoo Kim wrote:
> >>> On Tue, Jul 07, 2020 at 01:22:31PM +0200, Vlastimil Babka wrote:
> >>> 
> >>> Simply, I call memalloc_nocma_{save,restore} in new_non_cma_page(). It
> >>> would not cause any problem.
> >> 
> >> I believe a proper fix is the following. The scope is really defined for
> >> FOLL_LONGTERM pins and pushing it inside check_and_migrate_cma_pages
> >> will solve the problem as well but it imho makes more sense to do it in
> >> the caller the same way we do for any others. 
> >> 
> >> Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region")
> >
> > Agreed.
> >
> >> 
> >> I am not sure this is worth backporting to stable yet.
> >
> > CC Aneesh.
> >
> > Context: since check_and_migrate_cma_pages() calls __get_user_pages_locked(), it
> > should also be called under memalloc_nocma_save().
> 
> But by then we faulted in all relevant pages and migrated them out of
> CMA rea right?

check_and_migrate_cma_pages will allocate target pages that you want to
migrate off the CMA region unless I am misreading the code. And those
allocation need to be placed outside of the CMA.
-- 
Michal Hocko
SUSE Labs