From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id BA81A6B0006 for ; Fri, 23 Feb 2018 12:50:54 -0500 (EST) Received: by mail-io0-f199.google.com with SMTP id i129so8238518ioi.1 for ; Fri, 23 Feb 2018 09:50:54 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v23si2241515wmv.0.2018.02.23.09.50.53 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 23 Feb 2018 09:50:53 -0800 (PST) Date: Fri, 23 Feb 2018 18:50:51 +0100 From: Michal Hocko Subject: Re: [PATCH] Synchronize task mm counters on context switch Message-ID: <20180223175051.GX30681@dhcp22.suse.cz> References: <20180205220325.197241-1-dancol@google.com> <20180222001635.GB27147@rodete-desktop-imager.corp.google.com> <20180222020633.GC27147@rodete-desktop-imager.corp.google.com> <20180223081147.GD30773@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Colascione Cc: Minchan Kim , linux-mm@kvack.org, Andrew Morton , Oleg Nesterov , Peter Zijlstra On Fri 23-02-18 08:34:19, Daniel Colascione wrote: > On Fri, Feb 23, 2018 at 12:11 AM, Michal Hocko wrote: > > On Wed 21-02-18 18:49:35, Daniel Colascione wrote: > > [...] > >> For more context: on Android, we've historically scanned each processes's > >> address space using /proc/pid/smaps (and /proc/pid/smaps_rollup more > >> recently) to extract memory management statistics. We're looking at > >> replacing this mechanism with the new /proc/pid/status per-memory-type > >> (e.g., anonymous, file-backed) counters so that we can be even more > >> efficient, but we'd like the counts we collect to be accurate. > > > > If you need the accuracy then why don't you simply make > > SPLIT_RSS_COUNTING configurable and disable it in your setup? > > I considered that option, but it feels like a last resort. I think > agreement between /proc/pid/status and /proc/pid/smaps is a > correctness issue, and I'd prefer to fix the correctness issue > globally. But those counters are inherently out-of-sync because the data may be outdated as soon as you get the data back to the userspace (except for the trivial single threaded /proc/self/ case). > That said, *deleting* the SPLIT_RSS_COUNTING code would be nice and > simple. How sure are we that the per-task accounting is really needed? I have never measured that. 34e55232e59f ("mm: avoid false sharing of mm_counter") has _some_ numbers. > Maybe I'm wrong, but I feel like taking page faults will touch per-mm > data structures anyway, so one additional atomic update on the mm > shouldn't hurt all that much. I wouldn't be oppposed to remove it completely if it is not measureable. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org