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29 Jan 2020 13:57:35 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,379,1574150400"; d="scan'208";a="402120157" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga005.jf.intel.com with ESMTP; 29 Jan 2020 13:57:32 -0800 Date: Thu, 30 Jan 2020 05:57:45 +0800 From: Wei Yang To: Russell King - ARM Linux admin Cc: Dmitry Osipenko , Wei Yang , akpm@linux-foundation.org, dan.j.williams@intel.com, aneesh.kumar@linux.ibm.com, kirill@shutemov.name, yang.shi@linux.alibaba.com, thellstrom@vmware.com, Thierry Reding , Jon Hunter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "linux-tegra@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables() Message-ID: <20200129215745.GA20736@richard> Reply-To: Wei Yang References: <20200117232254.2792-1-richardw.yang@linux.intel.com> <20200117232254.2792-4-richardw.yang@linux.intel.com> <7147774a-14e9-4ff3-1548-4565f0d214d5@gmail.com> <20200129094738.GE25745@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200129094738.GE25745@shell.armlinux.org.uk> User-Agent: Mutt/1.9.4 (2018-02-28) 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 Wed, Jan 29, 2020 at 09:47:38AM +0000, Russell King - ARM Linux admin = wrote: >On Sun, Jan 26, 2020 at 05:47:57PM +0300, Dmitry Osipenko wrote: >> 18.01.2020 02:22, Wei Yang =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> > Use the general helper instead of do it by hand. >> >=20 >> > Signed-off-by: Wei Yang >> > --- >> > mm/mremap.c | 7 ++----- >> > 1 file changed, 2 insertions(+), 5 deletions(-) >> >=20 >> > diff --git a/mm/mremap.c b/mm/mremap.c >> > index c2af8ba4ba43..a258914f3ee1 100644 >> > --- a/mm/mremap.c >> > +++ b/mm/mremap.c >> > @@ -253,11 +253,8 @@ unsigned long move_page_tables(struct vm_area_s= truct *vma, >> > =20 >> > for (; old_addr < old_end; old_addr +=3D extent, new_addr +=3D ext= ent) { >> > cond_resched(); >> > - next =3D (old_addr + PMD_SIZE) & PMD_MASK; >> > - /* even if next overflowed, extent below will be ok */ >> > + next =3D pmd_addr_end(old_addr, old_end); >> > extent =3D next - old_addr; >> > - if (extent > old_end - old_addr) >> > - extent =3D old_end - old_addr; >> > old_pmd =3D get_old_pmd(vma->vm_mm, old_addr); >> > if (!old_pmd) >> > continue; >> > @@ -301,7 +298,7 @@ unsigned long move_page_tables(struct vm_area_st= ruct *vma, >> > =20 >> > if (pte_alloc(new_vma->vm_mm, new_pmd)) >> > break; >> > - next =3D (new_addr + PMD_SIZE) & PMD_MASK; >> > + next =3D pmd_addr_end(new_addr, new_addr + len); >> > if (extent > next - new_addr) >> > extent =3D next - new_addr; >> > move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, >> >=20 >>=20 >> Hello Wei, >>=20 >> Starting with next-20200122, I'm seeing the following in KMSG on NVIDI= A >> Tegra (ARM32): >>=20 >> BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:190 >>=20 >> and eventually kernel hangs. >>=20 >> Git's bisection points to this patch and reverting it helps. Please fi= x, >> thanks in advance. > >The above is definitely wrong - pXX_addr_end() are designed to be used >with an address index within the pXX table table and the address index >of either the last entry in the same pXX table or the beginning of the >_next_ pXX table. Arbitary end address indicies are not allowed. > #define pmd_addr_end(addr, end) \ ({ unsigned long __boundary =3D ((addr) + PMD_SIZE) & PMD_MASK; \ (__boundary - 1 < (end) - 1)? __boundary: (end); \ }) If my understanding is correct, the definition here align the addr to nex= t PMD boundary or end. I don't see the possibility to across another PMD. Do I miss something? >When page tables are "rolled up" when levels don't exist, it is common >practice for these macros to just return their end address index. >Hence, if they are used with arbitary end address indicies, then the >iteration will fail. > >The only way to do this is: > > next =3D pmd_addr_end(old_addr, > pud_addr_end(old_addr, > p4d_addr_end(old_addr, > pgd_addr_end(old_addr, old_end)))); > >which gives pmd_addr_end() (and each of the intermediate pXX_addr_end()) >the correct end argument. However, that's a more complex and verbose, >and likely less efficient than the current code. > >I'd suggest that there's nothing to "fix" in the v5.5 code wrt this, >and trying to "clean it up" will just result in less efficient or >broken code. > >--=20 >RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ >FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kb= ps up >According to speedtest.net: 11.9Mbps down 500kbps up --=20 Wei Yang Help you, Help me