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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_DKIMWL_WL_HIGH, USER_AGENT_MUTT autolearn=ham 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 88142C28CC2 for ; Wed, 29 May 2019 10:33:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 603F721721 for ; Wed, 29 May 2019 10:33:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559126037; bh=ZsJAgJ4qRGLyT8Xml+BEP7KR++7o2cnAdQ+/gcUsBLA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=PMpz3kFYvCVz9kDSoHUe46SoFAjCkBA8JrwV3iniGIPfEAfNdx4b9jbIkPTeQLLyT 4/JcpGDUppnmgaKO7jVmQMLZcrANZDgp14xhnHAvbgoAMslNXQqJvC0ejzrLC/ptnO KL9s+IQP98nLhtV+svZGx97nqbvv0WSkEvrmQg9g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726687AbfE2Kd4 (ORCPT ); Wed, 29 May 2019 06:33:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:36996 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725874AbfE2Kd4 (ORCPT ); Wed, 29 May 2019 06:33:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 50483AC40; Wed, 29 May 2019 10:33:54 +0000 (UTC) Date: Wed, 29 May 2019 12:33:52 +0200 From: Michal Hocko To: Daniel Colascione Cc: Minchan Kim , Andrew Morton , LKML , linux-mm , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Shakeel Butt , Sonny Rao , Brian Geffon , Linux API Subject: Re: [RFC 6/7] mm: extend process_madvise syscall to support vector arrary Message-ID: <20190529103352.GD18589@dhcp22.suse.cz> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-7-minchan@kernel.org> <20190520092258.GZ6836@dhcp22.suse.cz> <20190521024820.GG10039@google.com> <20190521062421.GD32329@dhcp22.suse.cz> <20190521102613.GC219653@google.com> <20190521103726.GM32329@dhcp22.suse.cz> <20190527074940.GB6879@google.com> 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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 29-05-19 03:08:32, Daniel Colascione wrote: > On Mon, May 27, 2019 at 12:49 AM Minchan Kim wrote: > > > > On Tue, May 21, 2019 at 12:37:26PM +0200, Michal Hocko wrote: > > > On Tue 21-05-19 19:26:13, Minchan Kim wrote: > > > > On Tue, May 21, 2019 at 08:24:21AM +0200, Michal Hocko wrote: > > > > > On Tue 21-05-19 11:48:20, Minchan Kim wrote: > > > > > > On Mon, May 20, 2019 at 11:22:58AM +0200, Michal Hocko wrote: > > > > > > > [Cc linux-api] > > > > > > > > > > > > > > On Mon 20-05-19 12:52:53, Minchan Kim wrote: > > > > > > > > Currently, process_madvise syscall works for only one address range > > > > > > > > so user should call the syscall several times to give hints to > > > > > > > > multiple address range. > > > > > > > > > > > > > > Is that a problem? How big of a problem? Any numbers? > > > > > > > > > > > > We easily have 2000+ vma so it's not trivial overhead. I will come up > > > > > > with number in the description at respin. > > > > > > > > > > Does this really have to be a fast operation? I would expect the monitor > > > > > is by no means a fast path. The system call overhead is not what it used > > > > > to be, sigh, but still for something that is not a hot path it should be > > > > > tolerable, especially when the whole operation is quite expensive on its > > > > > own (wrt. the syscall entry/exit). > > > > > > > > What's different with process_vm_[readv|writev] and vmsplice? > > > > If the range needed to be covered is a lot, vector operation makes senese > > > > to me. > > > > > > I am not saying that the vector API is wrong. All I am trying to say is > > > that the benefit is not really clear so far. If you want to push it > > > through then you should better get some supporting data. > > > > I measured 1000 madvise syscall vs. a vector range syscall with 1000 > > ranges on ARM64 mordern device. Even though I saw 15% improvement but > > absoluate gain is just 1ms so I don't think it's worth to support. > > I will drop vector support at next revision. > > Please do keep the vector support. Absolute timing is misleading, > since in a tight loop, you're not going to contend on mmap_sem. We've > seen tons of improvements in things like camera start come from > coalescing mprotect calls, with the gains coming from taking and > releasing various locks a lot less often and bouncing around less on > the contended lock paths. Raw throughput doesn't tell the whole story, > especially on mobile. This will always be a double edge sword. Taking a lock for longer can improve a throughput of a single call but it would make a latency for anybody contending on the lock much worse. Besides that, please do not overcomplicate the thing from the early beginning please. Let's start with a simple and well defined remote madvise alternative first and build a vector API on top with some numbers based on _real_ workloads. -- Michal Hocko SUSE Labs