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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6C124C433B4 for ; Mon, 19 Apr 2021 15:00:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37C146128C for ; Mon, 19 Apr 2021 15:00:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239385AbhDSPAh (ORCPT ); Mon, 19 Apr 2021 11:00:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:44764 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238029AbhDSPAh (ORCPT ); Mon, 19 Apr 2021 11:00:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1618844406; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Wif7xFamvaZAIzcaSwXiFOKU2ayIr8fdot8BMxjAWOs=; b=hnWLD+YYgLB1hJLch8Q0Us+SAQdF9bY2lARPYc+xgthdBTMLWOnNXdT2PXqo+COy6sGSZV rpUvHzVpK2ULuoPAyKjkv01PqHD4Pj1QC6hDzyI5FoDNQsfvNNu2mVCa0Ke+SqqeCS/cbM kco/IXaDcfPFu/KOLOV6ruIiArhFYyI= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E0D86B301; Mon, 19 Apr 2021 15:00:05 +0000 (UTC) Date: Mon, 19 Apr 2021 17:00:05 +0200 From: Michal Hocko To: Peter.Enderborg@sony.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, sumit.semwal@linaro.org, christian.koenig@amd.com, adobriyan@gmail.com, akpm@linux-foundation.org, songmuchun@bytedance.com, guro@fb.com, shakeelb@google.com, neilb@suse.de, samitolvanen@google.com, rppt@kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, willy@infradead.org Subject: Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo Message-ID: References: <20210417104032.5521-1-peter.enderborg@sony.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Mon 19-04-21 12:41:58, Peter.Enderborg@sony.com wrote: > On 4/19/21 2:16 PM, Michal Hocko wrote: > > On Sat 17-04-21 12:40:32, Peter Enderborg wrote: > >> This adds a total used dma-buf memory. Details > >> can be found in debugfs, however it is not for everyone > >> and not always available. dma-buf are indirect allocated by > >> userspace. So with this value we can monitor and detect > >> userspace applications that have problems. > > The changelog would benefit from more background on why this is needed, > > and who is the primary consumer of that value. > > > > I cannot really comment on the dma-buf internals but I have two remarks. > > Documentation/filesystems/proc.rst needs an update with the counter > > explanation and secondly is this information useful for OOM situations > > analysis? If yes then show_mem should dump the value as well. > > > > From the implementation point of view, is there any reason why this > > hasn't used the existing global_node_page_state infrastructure? > > I fix doc in next version.  Im not sure what you expect the commit message to include. As I've said. Usual justification covers answers to following questions - Why do we need it? - Why the existing data is insuficient? - Who is supposed to use the data and for what? I can see an answer for the first two questions (because this can be a lot of memory and the existing infrastructure is not production suitable - debugfs). But the changelog doesn't really explain who is going to use the new data. Is this a monitoring to raise an early alarm when the value grows? Is this for debugging misbehaving drivers? How is it valuable for those? > The function of the meminfo is: (From Documentation/filesystems/proc.rst) > > "Provides information about distribution and utilization of memory." True. Yet we do not export any random counters, do we? > Im not the designed of dma-buf, I think  global_node_page_state as a kernel > internal. It provides a node specific and optimized counters. Is this a good fit with your new counter? Or the NUMA locality is of no importance? > dma-buf is a device driver that provides a function so I might be > on the outside. However I also see that it might be relevant for a OOM. > It is memory that can be freed by killing userspace processes. > > The show_mem thing. Should it be a separate patch? This is up to you but if you want to expose the counter then send it in one series. -- Michal Hocko SUSE Labs