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Shutemov" To: Linus Torvalds Cc: Joel Fernandes , "Kirill A. Shutemov" , Andrew Morton , Linux-MM , Linux Kernel Mailing List , Naresh Kamboju , William Kucharski Subject: Re: [PATCHv2] mm: Fix warning in move_normal_pmd() Message-ID: <20200716131612.b7ottczdgnxwdvrp@box> References: <20200715135011.42743-1-kirill.shutemov@linux.intel.com> <20200715205428.GA201569@google.com> <20200715222228.jf2pv5u2wyhtc5o5@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: D71556C16 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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, Jul 15, 2020 at 04:18:44PM -0700, Linus Torvalds wrote: > On Wed, Jul 15, 2020 at 4:04 PM Linus Torvalds > wrote: > > > > It *might* be as simple as this incremental thing on top > > No, it needs to be > > + if (*old_addr + *len < old->vm_end) > + return; > > in try_to_align_end(), of course. Okay, this should work, but I'm not convinced that it gives much: number of cases covered by the optimization not going to be high. It can also lead to performance regression: for small mremap() if only one side of the range got aligned and there's no PMD_SIZE range to move, kernel will still iterate over PTEs, but it would need to handle more pte_none()s than without the patch. -- Kirill A. Shutemov