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=-2.2 required=3.0 tests=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 CEBB9C76195 for ; Thu, 18 Jul 2019 14:37:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6CB620873 for ; Thu, 18 Jul 2019 14:37:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390376AbfGROhE (ORCPT ); Thu, 18 Jul 2019 10:37:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50288 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726040AbfGROhE (ORCPT ); Thu, 18 Jul 2019 10:37:04 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8C258C09AD0F; Thu, 18 Jul 2019 14:37:02 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 14D3660576; Thu, 18 Jul 2019 14:36:59 +0000 (UTC) Subject: Re: [PATCH v2 2/2] mm, slab: Show last shrink time in us when slab/shrink is read To: Christopher Lameter Cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Roman Gushchin , Johannes Weiner , Shakeel Butt , Vladimir Davydov References: <20190717202413.13237-1-longman@redhat.com> <20190717202413.13237-3-longman@redhat.com> <0100016c04e1562a-e516c595-1d46-40df-ab29-da1709277e9a-000000@email.amazonses.com> From: Waiman Long Organization: Red Hat Message-ID: <6fb9f679-02d1-c33f-2d79-4c2eaa45d264@redhat.com> Date: Thu, 18 Jul 2019 10:36:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <0100016c04e1562a-e516c595-1d46-40df-ab29-da1709277e9a-000000@email.amazonses.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 18 Jul 2019 14:37:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/18/19 7:39 AM, Christopher Lameter wrote: > On Wed, 17 Jul 2019, Waiman Long wrote: > >> The show method of /sys/kernel/slab//shrink sysfs file currently >> returns nothing. This is now modified to show the time of the last >> cache shrink operation in us. > What is this useful for? Any use cases? I got query about how much time will the slab_mutex be held when shrinking the cache. I don't have a solid answer as it depends on how many memcg caches are there. This patch is a partial answer to that as it give a rough upper bound of the lock hold time. >> CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field >> is always available to the shrink methods. > Aside from minimal systems without CONFIG_SYSFS... Does this build without > CONFIG_SYSFS? The sysfs code in mm/slub.c is guarded by CONFIG_SLUB_DEBUG which, in turn, depends on CONFIG_SYSFS. So if CONFIG_SYSFS is off, the shrink sysfs methods will be off as well. I haven't tried doing a minimal build. I will certainly try that, but I don't expect any problem here. Cheers, Longman