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Violators will be prosecuted; Thu, 1 Mar 2018 07:17:52 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w217HpfH48300144; Thu, 1 Mar 2018 07:17:51 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 32F8911C05B; Thu, 1 Mar 2018 07:10:44 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EEC5D11C052; Thu, 1 Mar 2018 07:10:43 +0000 (GMT) Received: from mschwideX1 (unknown [9.145.179.24]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 1 Mar 2018 07:10:43 +0000 (GMT) Date: Thu, 1 Mar 2018 08:17:50 +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: <20180228223157.9281-1-willy@infradead.org> References: <20180228223157.9281-1-willy@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: 18030107-0012-0000-0000-000005B74FD3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18030107-0013-0000-0000-000019335278 Message-Id: <20180301081750.42b135c3@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=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803010094 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: 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.