From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp16.uk.ibm.com (e06smtp16.uk.ibm.com [195.75.94.112]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id A1FCC1A0037 for ; Mon, 1 Jun 2015 17:36:07 +1000 (AEST) Received: from /spool/local by e06smtp16.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 1 Jun 2015 08:36:03 +0100 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id C7A141B08069 for ; Mon, 1 Jun 2015 08:36:55 +0100 (BST) Received: from d06av05.portsmouth.uk.ibm.com (d06av05.portsmouth.uk.ibm.com [9.149.37.229]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t517a1Wl26738842 for ; Mon, 1 Jun 2015 07:36:01 GMT Received: from d06av05.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av05.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t517Zw7s028390 for ; Mon, 1 Jun 2015 01:36:01 -0600 Message-ID: <556C0B5D.40205@de.ibm.com> Date: Mon, 01 Jun 2015 09:35:57 +0200 From: Christian Borntraeger MIME-Version: 1.0 To: Dominik Dingel , linux-kernel@vger.kernel.org CC: Russell King , Catalin Marinas , Will Deacon , Tony Luck , Fenghua Yu , James Hogan , Ralf Baechle , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , linux390@de.ibm.com, "David S. Miller" , Chris Metcalf , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Andrew Morton , Zhang Zhen , David Rientjes , "Aneesh Kumar K.V" , Nathan Lynch , Andy Lutomirski , Michael Holzheu , Hugh Dickins , Naoya Horiguchi , Paolo Bonzini , "Jason J. Herne" , Davidlohr Bueso , "Kirill A. Shutemov" , Luiz Capitulino , Mike Kravetz , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/5] Remove s390 sw-emulated hugepages and cleanup References: <1432813957-46874-1-git-send-email-dingel@linux.vnet.ibm.com> In-Reply-To: <1432813957-46874-1-git-send-email-dingel@linux.vnet.ibm.com> Content-Type: text/plain; charset=iso-8859-15 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Am 28.05.2015 um 13:52 schrieb Dominik Dingel: > Hi everyone, > > there is a potential bug with KVM and hugetlbfs if the hardware does not > support hugepages (EDAT1). > We fix this by making EDAT1 a hard requirement for hugepages and > therefore removing and simplifying code. The cleanup itself is nice and probably the right thing to do. Emulating large pages makes the code more complex and asks for trouble (as outlined above) The only downside that I see is that z/VM as of today does not announce EDAT1 for its guests so the "emulated" large pages for hugetlbfs would be useful in that case. The current code allocates the page table only once and shares it for all mappers - which is useful for some big databases that spawn hundreds of processes with shared mappings of several hundred GBs. In these cases we do save a decent amount of page table memory. Not sure if that case is actually important, though. Christian