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 9C53AC28D13 for ; Tue, 23 Aug 2022 02:22:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239214AbiHWCWk (ORCPT ); Mon, 22 Aug 2022 22:22:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239350AbiHWCWf (ORCPT ); Mon, 22 Aug 2022 22:22:35 -0400 Received: from out1.migadu.com (out1.migadu.com [IPv6:2001:41d0:2:863f::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E5655B044; Mon, 22 Aug 2022 19:22:34 -0700 (PDT) Date: Mon, 22 Aug 2022 19:22:26 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1661221352; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TZOqb9ioXhJDay90SUSTe6Atr/mSmzrNsQskOLmcTw4=; b=jI0qftCBqUXZ/ZlfsIX0UQLffYq89HNRsd9OT0MrXYVBD4YWNdLsaPUXLt1Nt8conY9VNu Our9SMBCO6MRU92nM4eMoAvX1Z8XNGtZscdF3oPd/WL6APpO+wU/shrYeBfxkhKV2gs4cB 8Ikj1k7/usuDTGr3ZyOp6n5d4u0jScI= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Michal Hocko Cc: Shakeel Butt , Johannes Weiner , Muchun Song , Michal =?iso-8859-1?Q?Koutn=FD?= , Eric Dumazet , Soheil Hassas Yeganeh , Feng Tang , Oliver Sang , Andrew Morton , lkp@lists.01.org, cgroups@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] memcg: increase MEMCG_CHARGE_BATCH to 64 Message-ID: References: <20220822001737.4120417-1-shakeelb@google.com> <20220822001737.4120417-4-shakeelb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Aug 22, 2022 at 09:34:59PM +0200, Michal Hocko wrote: > On Mon 22-08-22 11:37:30, Roman Gushchin wrote: > [...] > > I wonder only if we want to make it configurable (Idk a sysctl or maybe > > a config option) and close the topic. > > I do not think this is a good idea. We have other examples where we have > outsourced internal tunning to the userspace and it has mostly proven > impractical and long term more problematic than useful (e.g. > lowmem_reserve_ratio, percpu_pagelist_high_fraction, swappiness just to > name some that come to my mind). I have seen more often these to be used > incorrectly than useful. A agree, not a strong opinion here. But I wonder if somebody will complain on Shakeel's change because of the reduced accuracy. I know some users are using memory cgroups to track the size of various workloads (including relatively small) and 32->64 pages per cpu change can be noticeable for them. But we can wait for an actual bug report :) > > In this case, I guess we should consider either moving to per memcg > charge batching and see whether the pcp overhead x memcg_count is worth > that or some automagic tuning of the batch size depending on how > effectively the batch is used. Certainly a lot of room for > experimenting. I'm not a big believer into the automagic tuning here because it's a fundamental trade-off of accuracy vs performance and various users might make a different choice depending on their needs, not on the cpu count or something else. Per-memcg batching sounds interesting though. For example, we can likely batch updates on leaf cgroups and have a single atomic update instead of multiple most of the times. Or do you mean something different? Thanks!