From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f197.google.com (mail-wj0-f197.google.com [209.85.210.197]) by kanga.kvack.org (Postfix) with ESMTP id 0469A6B0033 for ; Mon, 6 Feb 2017 08:24:15 -0500 (EST) Received: by mail-wj0-f197.google.com with SMTP id h7so18417573wjy.6 for ; Mon, 06 Feb 2017 05:24:14 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 13si902347wrb.315.2017.02.06.05.24.13 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 06 Feb 2017 05:24:13 -0800 (PST) Date: Mon, 6 Feb 2017 14:24:11 +0100 From: Michal Hocko Subject: Re: [PATCH 2/2 RESEND] mm: vmpressure: fix sending wrong events on underflow Message-ID: <20170206132410.GC10298@dhcp22.suse.cz> References: <1486383850-30444-1-git-send-email-vinmenon@codeaurora.org> <1486383850-30444-2-git-send-email-vinmenon@codeaurora.org> <20170206124037.GA10298@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: vinayak menon Cc: Vinayak Menon , Andrew Morton , Johannes Weiner , mgorman@techsingularity.net, vbabka@suse.cz, Rik van Riel , vdavydov.dev@gmail.com, anton.vorontsov@linaro.org, Minchan Kim , shashim@codeaurora.org, "linux-mm@kvack.org" , linux-kernel@vger.kernel.org On Mon 06-02-17 18:39:03, vinayak menon wrote: > On Mon, Feb 6, 2017 at 6:10 PM, Michal Hocko wrote: > > On Mon 06-02-17 17:54:10, Vinayak Menon wrote: > > [...] > >> diff --git a/mm/vmpressure.c b/mm/vmpressure.c > >> index 149fdf6..3281b34 100644 > >> --- a/mm/vmpressure.c > >> +++ b/mm/vmpressure.c > >> @@ -112,8 +112,10 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, > >> unsigned long reclaimed) > >> { > >> unsigned long scale = scanned + reclaimed; > >> - unsigned long pressure; > >> + unsigned long pressure = 0; > >> > >> + if (reclaimed >= scanned) > >> + goto out; > > > > This deserves a comment IMHO. Besides that, why shouldn't we normalize > > the result already in vmpressure()? Please note that the tree == true > > path will aggregate both scanned and reclaimed and that already skews > > numbers. > Sure. Will add a comment. > IIUC, normalizing in vmpressure() means something like this which you > mentioned in one > of your previous emails right ? > > + if (reclaimed > scanned) > + reclaimed = scanned; yes or scanned = reclaimed. > Considering a scan window of 512 pages and without above piece of > code, if the first scanning is of a THP page > Scan=1,Reclaimed=512 > If the next 511 scans results in 0 reclaimed pages > total_scan=512,Reclaimed=512 => vmpressure 0 I am not sure I understand. What do you mean by next scans? We do not modify counters outside of vmpressure? If you mean next iteration of shrink_node's loop then this changeshouldn't make a difference, no? > > Now with the above piece of code in place > Scan=1,Reclaimed=1, then > Scan=511, Reclaimed=0 > total_scan=512,Reclaimed=1 => critical vmpressure -- 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