From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id 24F406B0005 for ; Thu, 1 Mar 2018 02:17:58 -0500 (EST) Received: by mail-qt0-f197.google.com with SMTP id r18so2744777qtn.17 for ; Wed, 28 Feb 2018 23:17:58 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id w10si4014522qkg.351.2018.02.28.23.17.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Feb 2018 23:17:57 -0800 (PST) Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w2179UCS064022 for ; Thu, 1 Mar 2018 02:17:56 -0500 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0b-001b2d01.pphosted.com with ESMTP id 2gec4sswjv-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 01 Mar 2018 02:17:56 -0500 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 1 Mar 2018 07:17:54 -0000 Date: Thu, 1 Mar 2018 08:17:50 +0100 From: Martin Schwidefsky Subject: Re: [PATCH v3 0/4] Split page_type out from mapcount In-Reply-To: <20180228223157.9281-1-willy@infradead.org> References: <20180228223157.9281-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20180301081750.42b135c3@mschwideX1> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: linux-mm@kvack.org, Matthew Wilcox , linux-kernel@vger.kernel.org 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 ? -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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