Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755221AbdGKGAP (ORCPT ); Tue, 11 Jul 2017 02:00:15 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:36785 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751192AbdGKGAN (ORCPT ); Tue, 11 Jul 2017 02:00:13 -0400 Date: Tue, 11 Jul 2017 15:59:59 +1000 From: Balbir Singh To: Ram Pai Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, dave.hansen@intel.com, hbabu@us.ibm.com, arnd@arndb.de, akpm@linux-foundation.org, corbet@lwn.net, mingo@redhat.com Subject: Re: [RFC v5 02/38] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages Message-ID: <20170711155959.79e2d4de@firefly.ozlabs.ibm.com> In-Reply-To: <1499289735-14220-3-git-send-email-linuxram@us.ibm.com> References: <1499289735-14220-1-git-send-email-linuxram@us.ibm.com> <1499289735-14220-3-git-send-email-linuxram@us.ibm.com> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1524 Lines: 41 On Wed, 5 Jul 2017 14:21:39 -0700 Ram Pai wrote: > Rearrange 64K PTE bits to free up bits 3, 4, 5 and 6 > in the 64K backed HPTE pages. This along with the earlier > patch will entirely free up the four bits from 64K PTE. > The bit numbers are big-endian as defined in the ISA3.0 > > This patch does the following change to 64K PTE backed > by 64K HPTE. > > H_PAGE_F_SECOND (S) which occupied bit 4 moves to the > second part of the pte to bit 60. > H_PAGE_F_GIX (G,I,X) which occupied bit 5, 6 and 7 also > moves to the second part of the pte to bit 61, > 62, 63, 64 respectively > > since bit 7 is now freed up, we move H_PAGE_BUSY (B) from > bit 9 to bit 7. > > The second part of the PTE will hold > (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63. > > Before the patch, the 64K HPTE backed 64k PTE format was > as follows > > 0 1 2 3 4 5 6 7 8 9 10...........................63 > : : : : : : : : : : : : > v v v v v v v v v v v v > > ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-, > |x|x|x| |S |G |I |X |x|B|x|x|x|................|.|.|.|.| <- primary pte > '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_' > | | | | | | | | | | | | |..................| | | | | <- secondary pte > '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_' > It's not entirely clear what the secondary pte contains today and how many of the bits are free today? Balbir Singh.