From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752620AbdBCGRl (ORCPT ); Fri, 3 Feb 2017 01:17:41 -0500 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:58786 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752230AbdBCGRk (ORCPT ); Fri, 3 Feb 2017 01:17:40 -0500 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Fri, 3 Feb 2017 15:17:37 +0900 From: Minchan Kim To: Michal Hocko Cc: Vinayak Menon , akpm@linux-foundation.org, hannes@cmpxchg.org, mgorman@techsingularity.net, vbabka@suse.cz, riel@redhat.com, vdavydov.dev@gmail.com, anton.vorontsov@linaro.org, shashim@codeaurora.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure Message-ID: <20170203061737.GA32372@bbox> References: <1485504817-3124-1-git-send-email-vinmenon@codeaurora.org> <1485853328-7672-1-git-send-email-vinmenon@codeaurora.org> <20170202104422.GF22806@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170202104422.GF22806@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 02, 2017 at 11:44:22AM +0100, Michal Hocko wrote: > On Tue 31-01-17 14:32:08, Vinayak Menon wrote: > > During global reclaim, the nr_reclaimed passed to vmpressure > > includes the pages reclaimed from slab. But the corresponding > > scanned slab pages is not passed. This can cause total reclaimed > > pages to be greater than scanned, causing an unsigned underflow > > in vmpressure resulting in a critical event being sent to root > > cgroup. So do not consider reclaimed slab pages for vmpressure > > calculation. The reclaimed pages from slab can be excluded because > > the freeing of a page by slab shrinking depends on each slab's > > object population, making the cost model (i.e. scan:free) different > > from that of LRU. > > This might be true but what happens if the slab reclaim contributes > significantly to the overal reclaim? This would be quite rare but not > impossible. Of course, it is better for vmpressure to cover slab but it's not easy without page-based shrinking model, I think. It wold make vmpressure higher easily due to low reclaim efficiency compared to LRU pages. Yeah, vmpressure is not a perfect but no need to add more noises, either. It's regression since 6b4f7799c6a5 so I think this patch should go first and if someone want to cover slab really, he should spend a time to work it well. It's too much that Vinayak shuld make a effort for that.