From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 27A6E6B0008 for ; Thu, 1 Mar 2018 07:44:26 -0500 (EST) Received: by mail-wr0-f197.google.com with SMTP id 65so3971635wrn.7 for ; Thu, 01 Mar 2018 04:44:26 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id b10sor2718638edk.33.2018.03.01.04.44.24 for (Google Transport Security); Thu, 01 Mar 2018 04:44:24 -0800 (PST) Date: Thu, 1 Mar 2018 15:44:12 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH v3 0/4] Split page_type out from mapcount Message-ID: <20180301124412.gm6jxwzyfskzxspa@node.shutemov.name> References: <20180228223157.9281-1-willy@infradead.org> <20180301081750.42b135c3@mschwideX1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180301081750.42b135c3@mschwideX1> Sender: owner-linux-mm@kvack.org List-ID: To: Martin Schwidefsky Cc: Matthew Wilcox , linux-mm@kvack.org, Matthew Wilcox , linux-kernel@vger.kernel.org On Thu, Mar 01, 2018 at 08:17:50AM +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. Have you considered to use slab for page table allocation instead? IIRC some architectures practice this already. -- Kirill A. Shutemov -- 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