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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 C6AACC433F5 for ; Wed, 8 Sep 2021 18:03:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 487656115B for ; Wed, 8 Sep 2021 18:03:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 487656115B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 829B76B0071; Wed, 8 Sep 2021 14:03:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7D8DA6B0072; Wed, 8 Sep 2021 14:03:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6C75E6B0073; Wed, 8 Sep 2021 14:03:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0164.hostedemail.com [216.40.44.164]) by kanga.kvack.org (Postfix) with ESMTP id 595916B0071 for ; Wed, 8 Sep 2021 14:03:03 -0400 (EDT) Received: from smtpin37.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0479B182C7844 for ; Wed, 8 Sep 2021 18:03:03 +0000 (UTC) X-FDA: 78565177446.37.BC2DFDD Received: from mail-pg1-f175.google.com (mail-pg1-f175.google.com [209.85.215.175]) by imf01.hostedemail.com (Postfix) with ESMTP id ACBDE50505AB for ; Wed, 8 Sep 2021 18:03:02 +0000 (UTC) Received: by mail-pg1-f175.google.com with SMTP id s11so3440623pgr.11 for ; Wed, 08 Sep 2021 11:03:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=UGQvEXdrBVg53IK4NUbZnfU4dD2CNp4+2PmbwFjGdEc=; b=mocR2yuTelYjFHtGeDoBzetYTqgZHuinb4y5VmRpAM4dJCvhdag2Hy7i3f3nvnc6rO WYu6M0NnxnviSYR4sopLGv+yF/t9MZFKnfhMlBU1DKVEtwGlsNaDhId9w2UFeoXUOUK1 fsPraorqEVJ0g7RR6AMgv1AAi1fw/YkewYhfRzCJlHk3pL8i/ebUnEC4UD6sW/SBvf7P 2WU8Z4sl+2vTEHIknNSaB8SdMk+FwLqn6VgXPJ9FdhgtXgOSmQF8ZwCgUag318rzrgO0 rjbA7wFqfZk+ulO+Ez0lz9CkmR4zcTGgTdlfFew0EfayCCPuxXE3F/OdeEtxXzemgcVJ 7SaQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=UGQvEXdrBVg53IK4NUbZnfU4dD2CNp4+2PmbwFjGdEc=; b=BMtCV5eUL9CCABqZnzcv/9tCowGo3y28WsT+zvRLrooSS+71Db11iPoVnTwsFk2sQK 8heuaaFomz3fKrmXbQpT5JSP84iNHhtEWlekSUSnkXqd1AR43bIVaV52B6vN0x0PUEef 5aTnNayXfgNmvcC0I088tGN3YRbAeMc9XwIMlrCiCvFviKf6jr/7k2FlqgdY4d31E7Id SBZVl0z7TMS0ZbLWfPrkS/gSnyaIcdCoxa+sM39dUHD1Vl8NZOShSisA5exFL1ipgz0N Rm1VPrRlyT29aMSXiioxAMEQfr7nRe/iL0cG1ffTpoBAb1upfPs9H5ONUKSoiCiVF2xE p2Mg== X-Gm-Message-State: AOAM532ZTo3h4+jPhQMmpCGxH2TFwy+ivbvTr9oevYTkf1uXGsCt39On oNuR9CHctlMed/rE0Chp4gM= X-Google-Smtp-Source: ABdhPJzXQjQ0dLjy6o6xsIJhDMAqz2MvpxwnR6dDf4HHR6pWM/6IbxiKjFIawAvtJYvbH5F7Xb10Mg== X-Received: by 2002:a63:2343:: with SMTP id u3mr4942722pgm.100.1631124181392; Wed, 08 Sep 2021 11:03:01 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:500::4:97c5]) by smtp.gmail.com with ESMTPSA id n3sm2896375pfo.101.2021.09.08.11.02.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Sep 2021 11:03:00 -0700 (PDT) Date: Wed, 8 Sep 2021 11:02:58 -0700 From: Alexei Starovoitov To: Andrew Morton 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: <20210908180258.yjh62e5oouckar5b@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> <20210908105259.c47dcc4e4371ebb5e147ee6e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210908105259.c47dcc4e4371ebb5e147ee6e@linux-foundation.org> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: ACBDE50505AB X-Stat-Signature: hzfgow7e7zgbfuq95xfinzjjeht9abt7 Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=mocR2yuT; spf=pass (imf01.hostedemail.com: domain of alexei.starovoitov@gmail.com designates 209.85.215.175 as permitted sender) smtp.mailfrom=alexei.starovoitov@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1631124182-367366 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, Sep 08, 2021 at 10:52:59AM -0700, Andrew Morton wrote: > 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! Peter said: "The only sane approach is making the vma tree lockless, but so far the bpf people have resisted doing the right thing because they've been allowed to get away with these atrocities. " which is partially true. bpf folks didn't resist it. There is work ongoing to make it lockless. It just takes an long time. I don't see how bpf folks can speed it up any further. > Please describe the expected userspace-visible change from Peter's > patch in full detail? User space expects build_id to be available. Peter patch simply removes that feature. > 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? Just silence a lockdep as Yonghong proposed or some other way, since it's only a lockdep issue. There is no actual breakage. The feature was working and still works as intended.