From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932535AbbLCIy4 (ORCPT ); Thu, 3 Dec 2015 03:54:56 -0500 Received: from mail-wm0-f47.google.com ([74.125.82.47]:37087 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932446AbbLCIyy (ORCPT ); Thu, 3 Dec 2015 03:54:54 -0500 Date: Thu, 3 Dec 2015 09:54:52 +0100 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: memcg uncharge page counter mismatch Message-ID: <20151203085451.GC9264@dhcp22.suse.cz> References: <20151201133455.GB27574@bbox> <20151202101643.GC25284@dhcp22.suse.cz> <20151203013404.GA30779@bbox> <20151203021006.GA31041@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151203021006.GA31041@bbox> 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 03-12-15 11:10:06, Minchan Kim wrote: > On Thu, Dec 03, 2015 at 10:34:04AM +0900, Minchan Kim wrote: > > On Wed, Dec 02, 2015 at 11:16:43AM +0100, Michal Hocko wrote: > > > On Tue 01-12-15 22:34:55, Minchan Kim wrote: > > > > With new test on mmotm-2015-11-25-17-08, I saw below WARNING message > > > > several times. I couldn't see it with reverting new THP refcount > > > > redesign. > > > > > > Just a wild guess. What prevents migration/compaction from calling > > > split_huge_page on thp zero page? There is VM_BUG_ON but it is not clear > > > > I guess migration should work with LRU pages now but zero page couldn't > > stay there. Ahh, you are right. I have missed PageLRU check in isolate_migratepages_block pfn walker. > > > whether you run with CONFIG_DEBUG_VM enabled. > > > > I enabled VM_DEBUG_VM. > > > > > > > > Also, how big is the underflow? [...] > > nr_pages 293 new -324 > > nr_pages 16 new -340 > > nr_pages 342 new -91 > > nr_pages 246 new -337 > > nr_pages 15 new -352 > > nr_pages 15 new -367 They are quite large but that is not that surprising if we consider that we are batching many uncharges at once. > My guess is that it's related to new feature of Kirill's THP 'PageDoubleMap' > so a THP page could be mapped a pte but !pmd_trans_huge(*pmd) so memcg > precharge in move_charge should handle it? I am not familiar with the current state of THP after the rework unfortunately. So if I got you right then you are saying that pmd_trans_huge_lock fails to notice a THP so we will not charge it as THP and only charge one head page and then the tear down path will correctly recognize it as a THP and uncharge the full size, right? I have to admit I have no idea how PageDoubleMap works and how can pmd_trans_huge fail. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f49.google.com (mail-wm0-f49.google.com [74.125.82.49]) by kanga.kvack.org (Postfix) with ESMTP id BAC566B0038 for ; Thu, 3 Dec 2015 03:54:54 -0500 (EST) Received: by wmww144 with SMTP id w144so11564185wmw.1 for ; Thu, 03 Dec 2015 00:54:54 -0800 (PST) Received: from mail-wm0-f49.google.com (mail-wm0-f49.google.com. [74.125.82.49]) by mx.google.com with ESMTPS id l70si1918531wmb.75.2015.12.03.00.54.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Dec 2015 00:54:53 -0800 (PST) Received: by wmec201 with SMTP id c201so12448206wme.1 for ; Thu, 03 Dec 2015 00:54:53 -0800 (PST) Date: Thu, 3 Dec 2015 09:54:52 +0100 From: Michal Hocko Subject: Re: memcg uncharge page counter mismatch Message-ID: <20151203085451.GC9264@dhcp22.suse.cz> References: <20151201133455.GB27574@bbox> <20151202101643.GC25284@dhcp22.suse.cz> <20151203013404.GA30779@bbox> <20151203021006.GA31041@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151203021006.GA31041@bbox> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 03-12-15 11:10:06, Minchan Kim wrote: > On Thu, Dec 03, 2015 at 10:34:04AM +0900, Minchan Kim wrote: > > On Wed, Dec 02, 2015 at 11:16:43AM +0100, Michal Hocko wrote: > > > On Tue 01-12-15 22:34:55, Minchan Kim wrote: > > > > With new test on mmotm-2015-11-25-17-08, I saw below WARNING message > > > > several times. I couldn't see it with reverting new THP refcount > > > > redesign. > > > > > > Just a wild guess. What prevents migration/compaction from calling > > > split_huge_page on thp zero page? There is VM_BUG_ON but it is not clear > > > > I guess migration should work with LRU pages now but zero page couldn't > > stay there. Ahh, you are right. I have missed PageLRU check in isolate_migratepages_block pfn walker. > > > whether you run with CONFIG_DEBUG_VM enabled. > > > > I enabled VM_DEBUG_VM. > > > > > > > > Also, how big is the underflow? [...] > > nr_pages 293 new -324 > > nr_pages 16 new -340 > > nr_pages 342 new -91 > > nr_pages 246 new -337 > > nr_pages 15 new -352 > > nr_pages 15 new -367 They are quite large but that is not that surprising if we consider that we are batching many uncharges at once. > My guess is that it's related to new feature of Kirill's THP 'PageDoubleMap' > so a THP page could be mapped a pte but !pmd_trans_huge(*pmd) so memcg > precharge in move_charge should handle it? I am not familiar with the current state of THP after the rework unfortunately. So if I got you right then you are saying that pmd_trans_huge_lock fails to notice a THP so we will not charge it as THP and only charge one head page and then the tear down path will correctly recognize it as a THP and uncharge the full size, right? I have to admit I have no idea how PageDoubleMap works and how can pmd_trans_huge fail. -- 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