From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031635AbeCAPDX (ORCPT ); Thu, 1 Mar 2018 10:03:23 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57302 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031531AbeCAPDV (ORCPT ); Thu, 1 Mar 2018 10:03:21 -0500 Date: Thu, 1 Mar 2018 16:02:58 +0100 From: Martin Schwidefsky To: Matthew Wilcox Cc: "Kirill A. Shutemov" , 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: <20180301145058.GA19662@bombadil.infradead.org> References: <20180228223157.9281-1-willy@infradead.org> <20180301081750.42b135c3@mschwideX1> <20180301124412.gm6jxwzyfskzxspa@node.shutemov.name> <20180301145058.GA19662@bombadil.infradead.org> 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: 18030115-0020-0000-0000-000003FD61EC X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18030115-0021-0000-0000-000042919085 Message-Id: <20180301160258.6a619212@mschwideX1> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-01_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=2 malwarescore=0 lowpriorityscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803010189 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Mar 2018 06:50:58 -0800 Matthew Wilcox wrote: > On Thu, Mar 01, 2018 at 03:44:12PM +0300, Kirill A. Shutemov wrote: > > On Thu, Mar 01, 2018 at 08:17:50AM +0100, Martin Schwidefsky wrote: > > > 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. > > > > Have you considered to use slab for page table allocation instead? > > IIRC some architectures practice this already. > > You're not allowed to do that any more. Look at pgtable_page_ctor(), > or rather ptlock_init(). Oh yes, I forgot about the ptl. This takes up some fields in struct page which the slab/slub cache want to use as well. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.