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 11FB8ECAAD3 for ; Mon, 5 Sep 2022 18:07:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231671AbiIESHn (ORCPT ); Mon, 5 Sep 2022 14:07:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231162AbiIESHm (ORCPT ); Mon, 5 Sep 2022 14:07:42 -0400 Received: from mail-io1-xd30.google.com (mail-io1-xd30.google.com [IPv6:2607:f8b0:4864:20::d30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73CA458DF5 for ; Mon, 5 Sep 2022 11:07:37 -0700 (PDT) Received: by mail-io1-xd30.google.com with SMTP id r141so7297693iod.4 for ; Mon, 05 Sep 2022 11:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date; bh=Bum5cdqCm4gIf+I6AQy+wa1rXRQMNTd23PbVP2YAzEs=; b=P1Rb3fVwlXmtVf21S4DMQt260sMuniAXM5U5+atV+MhvCaumM2tXM3K6KXNyMSjZe0 3nRcAmBfF+7W6/WOVR2XOADKxyQte4OnojdLmDBhMFh9NdRikO81nZDemeys0l200+Ya BtEOzumSQwgu7ZWm3QeSZrXIo15d7vuotOaip8lu87RHKwjf3TUmogDdVvisjKKDmHLO PI+YQ7orIzFlOARyvXxCAIGW+yY5UcwZ3NgJ+U4tIgdfF/EioIbKjubkaR07oZSndJ0y pThgMzg7BhFJemuG5SPivo5QOLrPUeLBb55vYf5zQYtWTw5SjAAGq1FqYgp+ZLnBdvd/ Qr0g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date; bh=Bum5cdqCm4gIf+I6AQy+wa1rXRQMNTd23PbVP2YAzEs=; b=RVAcCBZbHLLgCFX/hwedX60lc0BeM/msbWG0+IbGtVdAcVXyeLycZCFPMtFKcsiYec 2Si7yPSRxgkgOtkgxhOLGGcapKQ/OBkPDnD+vc0SiT0GAXVugW+5L/cED1Eu1sghpa2H NyhYdFVmQFgM+Srv44OUKz0qfPivOQKjEQ14/1YqbLdQp9x/Mevt+WzjEimStbRZvqGG Sb2RMizMuh7kVdXmZRFqUZ6NtH7qn7S5jI74vTONkQvNAt51BqkjIBE2uyfdhtOWfFqU 4t1iifnDQ+Enana53nSHUdWD3fS1h0KmUG6dcq3dZ2AMhOz0YOIGh4c2yz39PoCWO/l8 /N4A== X-Gm-Message-State: ACgBeo26lApIEApzxUsEaxjqelyhEtQGe2HdLgneLgCFwPfXYNBi4zFR 89vv7wc4icU3aWtKuhi7hJJLfqdwHVv18Spci7m0jQ== X-Google-Smtp-Source: AA6agR6r5XgehoMYjBLme4+OWXroqyk9NqBwquoUHJYNtZV3MpkU67zLpVv3eXPms5QzjDOiUeZjqJqeUZuYSAeGarw= X-Received: by 2002:a05:6638:1492:b0:34c:d42:ac2f with SMTP id j18-20020a056638149200b0034c0d42ac2fmr13910620jak.305.1662401256621; Mon, 05 Sep 2022 11:07:36 -0700 (PDT) MIME-Version: 1.0 References: <20220830214919.53220-1-surenb@google.com> <20220831084230.3ti3vitrzhzsu3fs@moria.home.lan> <20220831101948.f3etturccmp5ovkl@suse.de> <20220831190154.qdlsxfamans3ya5j@moria.home.lan> In-Reply-To: From: Suren Baghdasaryan Date: Mon, 5 Sep 2022 11:07:25 -0700 Message-ID: Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications To: Marco Elver Cc: Michal Hocko , Kent Overstreet , Mel Gorman , Peter Zijlstra , Andrew Morton , Vlastimil Babka , Johannes Weiner , Roman Gushchin , Davidlohr Bueso , Matthew Wilcox , "Liam R. Howlett" , David Vernet , Juri Lelli , Laurent Dufour , Peter Xu , David Hildenbrand , Jens Axboe , mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com, ytcoode@gmail.com, Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Benjamin Segall , Daniel Bristot de Oliveira , Valentin Schneider , Christopher Lameter , Pekka Enberg , Joonsoo Kim , 42.hyeyoo@gmail.com, Alexander Potapenko , Dmitry Vyukov , Shakeel Butt , Muchun Song , arnd@arndb.de, jbaron@akamai.com, David Rientjes , Minchan Kim , Kalesh Singh , kernel-team , linux-mm , iommu@lists.linux.dev, kasan-dev@googlegroups.com, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-modules@vger.kernel.org, LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-bcache@vger.kernel.org On Mon, Sep 5, 2022 at 1:58 AM Marco Elver wrote: > > On Mon, 5 Sept 2022 at 10:12, Michal Hocko wrote: > > On Sun 04-09-22 18:32:58, Suren Baghdasaryan wrote: > > > On Thu, Sep 1, 2022 at 12:15 PM Michal Hocko wrote: > > [...] > > > > Yes, tracking back the call trace would be really needed. The question > > > > is whether this is really prohibitively expensive. How much overhead are > > > > we talking about? There is no free lunch here, really. You either have > > > > the overhead during runtime when the feature is used or on the source > > > > code level for all the future development (with a maze of macros and > > > > wrappers). > > > > > > As promised, I profiled a simple code that repeatedly makes 10 > > > allocations/frees in a loop and measured overheads of code tagging, > > > call stack capturing and tracing+BPF for page and slab allocations. > > > Summary: > > > > > > Page allocations (overheads are compared to get_free_pages() duration): > > > 6.8% Codetag counter manipulations (__lazy_percpu_counter_add + __alloc_tag_add) > > > 8.8% lookup_page_ext > > > 1237% call stack capture > > > 139% tracepoint with attached empty BPF program > > > > Yes, I am not surprised that the call stack capturing is really > > expensive comparing to the allocator fast path (which is really highly > > optimized and I suspect that with 10 allocation/free loop you mostly get > > your memory from the pcp lists). Is this overhead still _that_ visible > > for somehow less microoptimized workloads which have to take slow paths > > as well? > > > > Also what kind of stack unwinder is configured (I guess ORC)? This is > > not my area but from what I remember the unwinder overhead varies > > between ORC and FP. > > > > And just to make it clear. I do realize that an overhead from the stack > > unwinding is unavoidable. And code tagging would logically have lower > > overhead as it performs much less work. But the main point is whether > > our existing stack unwiding approach is really prohibitively expensive > > to be used for debugging purposes on production systems. I might > > misremember but I recall people having bigger concerns with page_owner > > memory footprint than the actual stack unwinder overhead. > > This is just to point out that we've also been looking at cheaper > collection of the stack trace (for KASAN and other sanitizers). The > cheapest way to unwind the stack would be a system with "shadow call > stack" enabled. With compiler support it's available on arm64, see > CONFIG_SHADOW_CALL_STACK. For x86 the hope is that at one point the > kernel will support CET, which newer Intel and AMD CPUs support. > Collecting the call stack would then be a simple memcpy. Thanks for the note Marco! I'll check out the CONFIG_SHADOW_CALL_STACK on Android.