From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935789AbeCAIA0 (ORCPT ); Thu, 1 Mar 2018 03:00:26 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:60360 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S934962AbeCAIAY (ORCPT ); Thu, 1 Mar 2018 03:00:24 -0500 Date: Thu, 1 Mar 2018 09:00:16 +0100 From: Martin Schwidefsky To: Matthew Wilcox Cc: linux-mm@kvack.org, Matthew Wilcox , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 0/4] Split page_type out from mapcount In-Reply-To: <20180301081750.42b135c3@mschwideX1> References: <20180228223157.9281-1-willy@infradead.org> <20180301081750.42b135c3@mschwideX1> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18030108-0020-0000-0000-000003FD34F5 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18030108-0021-0000-0000-0000429161C3 Message-Id: <20180301090016.01a54a5f@mschwideX1> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-01_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803010105 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Mar 2018 08:17:50 +0100 Martin Schwidefsky wrote: > On Wed, 28 Feb 2018 14:31:53 -0800 > Matthew Wilcox wrote: > > > From: Matthew Wilcox > > > > I want to use the _mapcount field to record what a page is in use as. > > This can help with debugging and we can also expose that information to > > userspace through /proc/kpageflags to help diagnose memory usage (not > > included as part of this patch set). > > > > First, we need s390 to stop using _mapcount for its own purposes; > > Martin, I hope you have time to look at this patch. I must confess I > > don't quite understand what the different bits are used for in the upper > > nybble of the _mapcount, but I tried to replicate what you were doing > > faithfully. > > Yeah, that is a nasty bit of code. On s390 we have 2K page tables (pte) > but 4K pages. If we use full pages for the pte tables we waste 2K of > memory for each of the tables. So we allocate 4K and split it into two > 2K pieces. Now we have to keep track of the pieces to be able to free > them again. > > I try to give your patch a spin today. It should be stand-alone, no ? Ok, that seems to work just fine. System boots and survived some stress without loosing memory. Acked-by: Martin Schwidefsky -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.