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[37.188.135.150]) by smtp.gmail.com with ESMTPSA id o9sm6493018wrx.48.2020.03.23.00.34.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2020 00:34:10 -0700 (PDT) Date: Mon, 23 Mar 2020 08:34:08 +0100 From: Michal Hocko To: Pingfan Liu Cc: linux-mm@kvack.org, =?iso-8859-1?B?Suly9G1l?= Glisse , John Hubbard , "Kirill A . Shutemov" , Aneesh Kumar , Andrew Morton Subject: Re: [PATCH] mm/rmap: fix the handling of device private page in try_to_unmap_one() Message-ID: <20200323073408.GA7524@dhcp22.suse.cz> References: <1584885427-4952-1-git-send-email-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1584885427-4952-1-git-send-email-kernelfans@gmail.com> Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun 22-03-20 21:57:07, Pingfan Liu wrote: > For zone_device, migration can only happen on is_device_private_page(pa= ge). > Correct the logic in try_to_unmap_one(). Maybe it is just me lacking knowledge in the zone_device ZOO. But this really deserves a much more detailed explanation IMHO. It seems a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") deliberately made the decision to allow unmapping these pages? Is the check just wrong, inncomplete? Why? What is the real user visible problem here? =20 > Signed-off-by: Pingfan Liu > Cc: J=E9r=F4me Glisse > Cc: Michal Hocko > Cc: John Hubbard > Cc: Kirill A. Shutemov > Cc: Aneesh Kumar > Cc: Andrew Morton > To: linux-mm@kvack.org > --- > mm/rmap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/mm/rmap.c b/mm/rmap.c > index b838647..ffadf3e 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1380,7 +1380,7 @@ static bool try_to_unmap_one(struct page *page, s= truct vm_area_struct *vma, >=20 > if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) && > is_zone_device_page(page) && !is_device_private_page(page)) > - return true; > + return false; >=20 > if (flags & TTU_SPLIT_HUGE_PMD) { > split_huge_pmd_address(vma, address, > @@ -1487,7 +1487,7 @@ static bool try_to_unmap_one(struct page *page, s= truct vm_area_struct *vma, >=20 > if (IS_ENABLED(CONFIG_MIGRATION) && > (flags & TTU_MIGRATION) && > - is_zone_device_page(page)) { > + is_device_private_page(page)) { > swp_entry_t entry; > pte_t swp_pte; >=20 > -- > 2.7.5 --=20 Michal Hocko SUSE Labs