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=-7.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=no 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 57166C433F5 for ; Wed, 8 Sep 2021 17:53:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D93156113D for ; Wed, 8 Sep 2021 17:53:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D93156113D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 1098C6B0071; Wed, 8 Sep 2021 13:53:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0B9FF6B0072; Wed, 8 Sep 2021 13:53:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EEA2F900002; Wed, 8 Sep 2021 13:53:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0105.hostedemail.com [216.40.44.105]) by kanga.kvack.org (Postfix) with ESMTP id DB4186B0071 for ; Wed, 8 Sep 2021 13:53:01 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 7A53B8249980 for ; Wed, 8 Sep 2021 17:53:01 +0000 (UTC) X-FDA: 78565152162.14.CC986EA Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf11.hostedemail.com (Postfix) with ESMTP id 225CFF0000B8 for ; Wed, 8 Sep 2021 17:53:00 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id C457061051; Wed, 8 Sep 2021 17:52:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1631123580; bh=nXi0yLf9rlDTWkxbPehUsFIjHiAj8b4Mhco6ObvEQQs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=SwXdm8kZaKD1urXqfdWpupnvojRaYRYjV8ng4kZVRSVAujp3J0MUwY9w75u6t1U+A 2zefi/f9lmiHRf+GffrxwcTKNAzHr2OuxQlxHM8cNC24uFmmMxqoIYUQQ0EwJs05Ix rOMrYZ7n1E8F/JI5b5UYccyyueGR+epgkindDFVQ= Date: Wed, 8 Sep 2021 10:52:59 -0700 From: Andrew Morton To: Alexei Starovoitov Cc: Luigi Rizzo , Yonghong Song , Liam Howlett , Peter Zijlstra , Jason Gunthorpe , Daniel Borkmann , Michel Lespinasse , bpf , "linux-mm@kvack.org" , Alexei Starovoitov , Andrii Nakryiko , "kernel-team@fb.com" Subject: Re: [PATCH mm/bpf v2] mm: bpf: add find_vma_no_check() without lockdep_assert on mm->mmap_lock Message-Id: <20210908105259.c47dcc4e4371ebb5e147ee6e@linux-foundation.org> In-Reply-To: <20210908172118.n2f4w7epm6hh62zf@ast-mbp.dhcp.thefacebook.com> References: <20210908044427.3632119-1-yhs@fb.com> <20210908135326.GZ1200268@ziepe.ca> <20210908151230.m2zyslt4qrufm4bv@revolver> <20210908172118.n2f4w7epm6hh62zf@ast-mbp.dhcp.thefacebook.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=SwXdm8kZ; spf=pass (imf11.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 225CFF0000B8 X-Stat-Signature: 74z1o35bzbguyu7r5kyf7irjnin87kfp X-HE-Tag: 1631123580-604662 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, 8 Sep 2021 10:21:18 -0700 Alexei Starovoitov wrote: > > Again I am ignorant on the details so if you can clarify the following > > it may help me and others to better understand the problem: > > > > 1. Peter's patch appears to just take the same "fallback" path > > that would be taken if the trylock failed. > > Is this really a breakage or just loss of performance ? > > I would expect the latter, since it is called "fallback". > > As Yonghong explained it's a user space breakage. > User space tooling expects build_id to be available 99.999% of the time > and that's what users observed in practice. > They've built a bunch of tools on top of this feature. > The data from these tools goes into various datacenter tables > and humans analyze it later. > So Peter's proposal is not acceptable. We don't want to get yelled at. > I'm not understanding. Peter said "this patch merely removes a performance tweak" and you and Yonghong said "it breaks userspace". These assertions are contradictory! Please describe the expected userspace-visible change from Peter's patch in full detail? And yes, it is far preferable that we resolve this by changing BPF to be a better interface citizen, please. Let's put those thinking caps on?