From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A6B1C74A5B for ; Tue, 21 Mar 2023 11:31:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230095AbjCULbM (ORCPT ); Tue, 21 Mar 2023 07:31:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbjCULbK (ORCPT ); Tue, 21 Mar 2023 07:31:10 -0400 Received: from elvis.franken.de (elvis.franken.de [193.175.24.41]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id CF06930DD; Tue, 21 Mar 2023 04:31:05 -0700 (PDT) Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1peaCj-0003H6-00; Tue, 21 Mar 2023 12:31:01 +0100 Received: by alpha.franken.de (Postfix, from userid 1000) id 0EE4EC1B11; Tue, 21 Mar 2023 12:30:16 +0100 (CET) Date: Tue, 21 Mar 2023 12:30:15 +0100 From: Thomas Bogendoerfer To: Matthew Wilcox Cc: linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org Subject: Re: [PATCH v4 16/36] mips: Implement the new page table range API Message-ID: <20230321113015.GA11292@alpha.franken.de> References: <20230315051444.3229621-1-willy@infradead.org> <20230315051444.3229621-17-willy@infradead.org> <20230315105022.GA9850@alpha.franken.de> <20230317152920.GA11653@alpha.franken.de> <20230319184536.GA6491@alpha.franken.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 19, 2023 at 08:16:36PM +0000, Matthew Wilcox wrote: > On Sun, Mar 19, 2023 at 07:45:36PM +0100, Thomas Bogendoerfer wrote: > > On Fri, Mar 17, 2023 at 04:29:20PM +0100, Thomas Bogendoerfer wrote: > > > hmm, not sure if that would help. R4k style TLB has two PTEs mapped > > > per TLB entry. So by advancing per page __update_tlb() is called more > > > often than needed. > > > > btw. how big is nr going to be ? There are MIPS SoCs out there, which > > just have 16 TLBs... > > Oof. The biggest we're going to see for now is one less than PTRS_PER_PMD > (that'd be a PMD-sized allocation that's mapped askew with 1 page in > one PMD and n-1 pages in the adjacent PMD). That'd be 511 on x86 and > I presume something similar on MIPS. More than 16, for sure. biggest TLB I could find is 256 entries, which can map 512 pages. > Now, this isn't a new problem with this patchset. With fault-around, > we already call set_pte_at() N times. And we don't say which ones are > speculative entries vs the one actually faulted in. ic > But let's see if we can fix it. What if we passed in the vmf? That would > give you the actual faulting address, so you'd know to only put the PTE > into the Linux page tables and not go as far as putting it into the TLB. > Open to other ideas. that would help to optimize the case. But update_mmu_cache_range needs to do __update_tlb() for every page to avoid stale data in TLB. If I understood correctly only the way how TLB updates are done changed, so there shouldn't be performance regressions. And optimizing like moving the looping over the pages into __update_tlb() could be done in a second step. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]