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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 56F82C433C1 for ; Tue, 30 Mar 2021 16:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2414861994 for ; Tue, 30 Mar 2021 16:58:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232261AbhC3Q5j (ORCPT ); Tue, 30 Mar 2021 12:57:39 -0400 Received: from verein.lst.de ([213.95.11.211]:59774 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232048AbhC3Q50 (ORCPT ); Tue, 30 Mar 2021 12:57:26 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id F061768B02; Tue, 30 Mar 2021 18:57:23 +0200 (CEST) Date: Tue, 30 Mar 2021 18:57:23 +0200 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] blktrace: limit allowed total trace buffer size Message-ID: <20210330165723.GB13829@lst.de> References: <20210323081440.81343-1-ming.lei@redhat.com> <20210323081440.81343-3-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210323081440.81343-3-ming.lei@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Mar 23, 2021 at 04:14:40PM +0800, Ming Lei wrote: > On some ARCHs, such as aarch64, page size may be 64K, meantime there may Which we call arm64.. > be lots of CPU cores. relay_open() needs to allocate pages on each CPU > blktrace, so easily too many pages are taken by blktrace. For example, > on one ARM64 server: 224 CPU cores, 16G RAM, blktrace finally got > allocated 7GB in case of 'blktrace -b 8192' which is used by device-mapper > test suite[1]. This way could cause OOM easily. > > Fix the issue by limiting max allowed pages to be 1/8 of totalram_pages(). Doesn't this break the blktrace ABI by using different buffer size and numbers than the user asked for? I think we can enforce an upper limit and error out, but silently adjusting seems wrong. Wouldn't it make more sense to fix userspace to not request so many and so big buffers instead?