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 X-Spam-Level: X-Spam-Status: No, score=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 39BFEC433B4 for ; Mon, 19 Apr 2021 09:36:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 169B760FF3 for ; Mon, 19 Apr 2021 09:36:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238592AbhDSJhH (ORCPT ); Mon, 19 Apr 2021 05:37:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:39896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237771AbhDSJhH (ORCPT ); Mon, 19 Apr 2021 05:37:07 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CE5486101D; Mon, 19 Apr 2021 09:36:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618824997; bh=gKvvGKT7gwRRGsoZvfcNRGcz0Uq+afSf3EpowR/OLNc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P3lkwvjW/R0feyjsaGtC46WUvSA5fINd83XuQt+ZESQgLmLjszsOUu+LDUHEcKzFK sigplCcojQ4mBEu6rER8dXQGEZqUGKDoigx7QfRx9QLVtR+aRgfcwkGniPnNZcwK1Y esYRQZkAPosCP1G+VuLB3y59ckxByt6ogqqNClQC0M2eiZ92c2ENWNcdwDNmkJaobH Q6eesP5D30kBeyc+SuhpDLAJuFI3pxzWfEnJtG1/zLkGk9o8TBN3uAS9cvmcCI24LT EfVn9mOhYvqkGR2hQgso12puyTHP9lzT9F9imFG/PQhcsS3AMAg4DeKSgo5cUC9n88 820gRflNkMWuw== Date: Mon, 19 Apr 2021 12:36:19 +0300 From: Mike Rapoport To: David Hildenbrand Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Matthew Garrett , Mark Rutland , Michal Hocko , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , "Rafael J. Wysocki" , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , Yury Norov , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org, kernel test robot Subject: Re: [PATCH] secretmem: optimize page_is_secretmem() Message-ID: References: <20210419084218.7466-1-rppt@kernel.org> <3b30ac54-8a92-5f54-28f0-f110a40700c7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3b30ac54-8a92-5f54-28f0-f110a40700c7@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Mon, Apr 19, 2021 at 11:15:02AM +0200, David Hildenbrand wrote: > On 19.04.21 10:42, Mike Rapoport wrote: > > From: Mike Rapoport > > > > Kernel test robot reported -4.2% regression of will-it-scale.per_thread_ops > > due to commit "mm: introduce memfd_secret system call to create "secret" > > memory areas". > > > > The perf profile of the test indicated that the regression is caused by > > page_is_secretmem() called from gup_pte_range() (inlined by gup_pgd_range): > > > > 27.76 +2.5 30.23 perf-profile.children.cycles-pp.gup_pgd_range > > 0.00 +3.2 3.19 ± 2% perf-profile.children.cycles-pp.page_mapping > > 0.00 +3.7 3.66 ± 2% perf-profile.children.cycles-pp.page_is_secretmem > > > > Further analysis showed that the slow down happens because neither > > page_is_secretmem() nor page_mapping() are not inline and moreover, > > multiple page flags checks in page_mapping() involve calling > > compound_head() several times for the same page. > > > > Make page_is_secretmem() inline and replace page_mapping() with page flag > > checks that do not imply page-to-head conversion. > > > > Reported-by: kernel test robot > > Signed-off-by: Mike Rapoport > > --- > > > > @Andrew, > > The patch is vs v5.12-rc7-mmots-2021-04-15-16-28, I'd appreciate if it would > > be added as a fixup to the memfd_secret series. > > > > include/linux/secretmem.h | 26 +++++++++++++++++++++++++- > > mm/secretmem.c | 12 +----------- > > 2 files changed, 26 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > > index 907a6734059c..b842b38cbeb1 100644 > > --- a/include/linux/secretmem.h > > +++ b/include/linux/secretmem.h > > @@ -4,8 +4,32 @@ > > #ifdef CONFIG_SECRETMEM > > +extern const struct address_space_operations secretmem_aops; > > + > > +static inline bool page_is_secretmem(struct page *page) > > +{ > > + struct address_space *mapping; > > + > > + /* > > + * Using page_mapping() is quite slow because of the actual call > > + * instruction and repeated compound_head(page) inside the > > + * page_mapping() function. > > + * We know that secretmem pages are not compound and LRU so we can > > + * save a couple of cycles here. > > + */ > > + if (PageCompound(page) || !PageLRU(page)) > > + return false; > > I'd assume secretmem pages are rare in basically every setup out there. So > maybe throwing in a couple of likely()/unlikely() might make sense. I'd say we could do unlikely(page_is_secretmem()) at call sites. Here I can hardly estimate which pages are going to be checked. > > + > > + mapping = (struct address_space *) > > + ((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS); > > + > > Not sure if open-coding page_mapping is really a good idea here -- or even > necessary after the fast path above is in place. Anyhow, just my 2 cents. Well, most if the -4.2% of the performance regression kbuild reported were due to repeated compount_head(page) in page_mapping(). So the whole point of this patch is to avoid calling page_mapping(). > The idea of the patch makes sense to me. -- Sincerely yours, Mike.