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Shutemov" To: Wei Yang Cc: akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com, vbabka@suse.cz, willy@infradead.org, thomas_os@shipmail.org, thellstrom@vmware.com, anshuman.khandual@arm.com, sean.j.christopherson@intel.com, aneesh.kumar@linux.ibm.com, peterx@redhat.com, walken@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, digetx@gmail.com Subject: Re: [RESEND Patch v2 3/4] mm/mremap: calculate extent in one place Message-ID: <20200707104722.j3awgkz4ncgm2bss@box> References: <20200626135216.24314-1-richard.weiyang@linux.alibaba.com> <20200626135216.24314-4-richard.weiyang@linux.alibaba.com> <20200706100729.y2wbkpc4tyvjojzg@box> <20200707013856.GA27805@L-31X9LVDL-1304.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200707013856.GA27805@L-31X9LVDL-1304.local> X-Rspamd-Queue-Id: DDDAF10043E76 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 07, 2020 at 09:38:56AM +0800, Wei Yang wrote: > On Mon, Jul 06, 2020 at 01:07:29PM +0300, Kirill A. Shutemov wrote: > >On Fri, Jun 26, 2020 at 09:52:15PM +0800, Wei Yang wrote: > >> Page tables is moved on the base of PMD. This requires both source > >> and destination range should meet the requirement. > >> > >> Current code works well since move_huge_pmd() and move_normal_pmd() > >> would check old_addr and new_addr again. And then return to move_ptes() > >> if the either of them is not aligned. > >> > >> In stead of calculating the extent separately, it is better to calculate > >> in one place, so we know it is not necessary to try move pmd. By doing > >> so, the logic seems a little clear. > >> > >> Signed-off-by: Wei Yang > >> Tested-by: Dmitry Osipenko > >> --- > >> mm/mremap.c | 6 +++--- > >> 1 file changed, 3 insertions(+), 3 deletions(-) > >> > >> diff --git a/mm/mremap.c b/mm/mremap.c > >> index de27b12c8a5a..a30b3e86cc99 100644 > >> --- a/mm/mremap.c > >> +++ b/mm/mremap.c > >> @@ -258,6 +258,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma, > >> extent = next - old_addr; > >> if (extent > old_end - old_addr) > >> extent = old_end - old_addr; > >> + next = (new_addr + PMD_SIZE) & PMD_MASK; > > > >Please use round_up() for both 'next' calculations. > > > > I took another close look into this, seems this is not a good suggestion. > > round_up(new_addr, PMD_SIZE) > > would be new_addr when new_addr is PMD_SIZE aligned, which is not what we > expect. Maybe round_down(new_addr + PMD_SIZE, PMD_SIZE)? -- Kirill A. Shutemov