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=-12.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 DC198C43462 for ; Thu, 15 Apr 2021 18:47:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF6B161152 for ; Thu, 15 Apr 2021 18:47:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234641AbhDOSsB (ORCPT ); Thu, 15 Apr 2021 14:48:01 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:36807 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234505AbhDOSr7 (ORCPT ); Thu, 15 Apr 2021 14:47:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618512455; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YhU7TCQFVSEb9BISH8yUV4uS7YEP0B0LlCGjPhsfIjk=; b=RHiDO3VVOHh2cnqVGwB19qxEhTKswqcaTc1HJSmXceVJ+18iJA+RDSoWlo58AItVpahRxH LHrk50W1b8Zv5NtnlYG7OumxQofHWk22/2MIfH55nRz0ImrJYs+cYCAcZgC0pbbdjazpqM ZjsASs5rzXqXm27NuV9yRR0d/SBsItk= Received: from mail-qt1-f197.google.com (mail-qt1-f197.google.com [209.85.160.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-239-RnAw17uYPOC-A81ar37W2Q-1; Thu, 15 Apr 2021 14:47:34 -0400 X-MC-Unique: RnAw17uYPOC-A81ar37W2Q-1 Received: by mail-qt1-f197.google.com with SMTP id i9-20020ac85e490000b02901b186fa5716so4612291qtx.22 for ; Thu, 15 Apr 2021 11:47:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=YhU7TCQFVSEb9BISH8yUV4uS7YEP0B0LlCGjPhsfIjk=; b=JKR3+pGex90kx7lWrl16o1SSHCYOX2ftBTwxD3l9InbXCNc8K7ieOQwLjjBqJ7Goop mDRugXs9YcjTqfs6H/9BiMawZqeQ+QL5dl03RcU6bnwsc2no2LG8FbgZ81aElpXSNr6r IPacYtUzpFkCj5OT/9ObVlxO2/HPJ4xdpaKj7Qlc0dYWGbL6upfyRqRM+U5QJ8GfB/HV vYVeIjzywi20qRvrebDbZkZILjbiYuT38FaJFJxrUa3OBtm4Xvb8QeQuK9oRz3WYDIhL /EFJmBahj5qyB/Zh1zydtEeOl1r/ZRpvep4QXcs7bUktgGeAHqTeV2LGA0Y0iZDg86TR KlBw== X-Gm-Message-State: AOAM532mMyQWzF2J9ZwHnZk9NFT/RqZojTrxgI3YGdGf3bai3/Z8Nk0K z43NPN1BLY/80ZCxF9BAtX0RhNpNOX/t4Al7jA6yssdq1DAHOmFXntCldQ/K9p2g7YDB2d2eW5x Mfdmki184nHoGAOFvbBcgeJmk X-Received: by 2002:a37:46d5:: with SMTP id t204mr4781190qka.211.1618512453589; Thu, 15 Apr 2021 11:47:33 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxUdX6JKkD3hF7Cdh86JsrrLjUwoikG2qPfbSEJduJ0S04O2Lz1qwFCwKtpktu1s8vKKzSdEQ== X-Received: by 2002:a37:46d5:: with SMTP id t204mr4781179qka.211.1618512453403; Thu, 15 Apr 2021 11:47:33 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id c23sm2489546qkk.24.2021.04.15.11.47.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Apr 2021 11:47:33 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH v3 2/5] mm/memcg: Introduce obj_cgroup_uncharge_mod_state() To: Johannes Weiner , Waiman Long Cc: Michal Hocko , Vladimir Davydov , Andrew Morton , Tejun Heo , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Muchun Song , Alex Shi , Chris Down , Yafang Shao , Wei Yang , Masayoshi Mizuma , Xing Zhengjun References: <20210414012027.5352-1-longman@redhat.com> <20210414012027.5352-3-longman@redhat.com> <1c85e8f6-e8b9-33e1-e29b-81fbadff959f@redhat.com> Message-ID: <8a104fd5-64c7-3f41-981c-9cfa977c78a6@redhat.com> Date: Thu, 15 Apr 2021 14:47:31 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/15/21 2:10 PM, Johannes Weiner wrote: > On Thu, Apr 15, 2021 at 12:35:45PM -0400, Waiman Long wrote: >> On 4/15/21 12:30 PM, Johannes Weiner wrote: >>> On Tue, Apr 13, 2021 at 09:20:24PM -0400, Waiman Long wrote: >>>> In memcg_slab_free_hook()/pcpu_memcg_free_hook(), obj_cgroup_uncharge() >>>> is followed by mod_objcg_state()/mod_memcg_state(). Each of these >>>> function call goes through a separate irq_save/irq_restore cycle. That >>>> is inefficient. Introduce a new function obj_cgroup_uncharge_mod_state() >>>> that combines them with a single irq_save/irq_restore cycle. >>>> >>>> @@ -3292,6 +3296,25 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size) >>>> refill_obj_stock(objcg, size); >>>> } >>>> +void obj_cgroup_uncharge_mod_state(struct obj_cgroup *objcg, size_t size, >>>> + struct pglist_data *pgdat, int idx) >>> The optimization makes sense. >>> >>> But please don't combine independent operations like this into a >>> single function. It makes for an unclear parameter list, it's a pain >>> in the behind to change the constituent operations later on, and it >>> has a habit of attracting more random bools over time. E.g. what if >>> the caller already has irqs disabled? What if it KNOWS that irqs are >>> enabled and it could use local_irq_disable() instead of save? >>> >>> Just provide an __obj_cgroup_uncharge() that assumes irqs are >>> disabled, combine with the existing __mod_memcg_lruvec_state(), and >>> bubble the irq handling up to those callsites which know better. >>> >> That will also work. However, the reason I did that was because of patch 5 >> in the series. I could put the get_obj_stock() and put_obj_stock() code in >> slab.h and allowed them to be used directly in various places, but hiding in >> one function is easier. > Yeah it's more obvious after getting to patch 5. > > But with the irq disabling gone entirely, is there still an incentive > to combine the atomic section at all? Disabling preemption is pretty > cheap, so it wouldn't matter to just do it twice. > > I.e. couldn't the final sequence in slab code simply be > > objcg_uncharge() > mod_objcg_state() > > again and each function disables preemption (and in the rare case > irqs) as it sees fit? > > You lose the irqsoff batching in the cold path, but as you say, hit > rates are pretty good, and it doesn't seem worth complicating the code > for the cold path. > That does make sense, though a little bit of performance may be lost. I will try that out to see how it work out performance wise. Cheers, Longman