From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id DC1956B0524 for ; Tue, 11 Jul 2017 11:44:35 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id r103so955859wrb.0 for ; Tue, 11 Jul 2017 08:44:35 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id v67si2013269wma.175.2017.07.11.08.44.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jul 2017 08:44:34 -0700 (PDT) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6BFiB9n063720 for ; Tue, 11 Jul 2017 11:44:33 -0400 Received: from e31.co.us.ibm.com (e31.co.us.ibm.com [32.97.110.149]) by mx0b-001b2d01.pphosted.com with ESMTP id 2bn0mv2myj-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 11 Jul 2017 11:44:32 -0400 Received: from localhost by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 11 Jul 2017 09:44:32 -0600 Date: Tue, 11 Jul 2017 08:44:15 -0700 From: Ram Pai Subject: Re: [RFC v5 02/38] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages Reply-To: Ram Pai References: <1499289735-14220-1-git-send-email-linuxram@us.ibm.com> <1499289735-14220-3-git-send-email-linuxram@us.ibm.com> <20170711155959.79e2d4de@firefly.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170711155959.79e2d4de@firefly.ozlabs.ibm.com> Message-Id: <20170711154415.GA5525@ram.oc3035372033.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Balbir Singh 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 On Tue, Jul 11, 2017 at 03:59:59PM +1000, Balbir Singh wrote: > 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? The secondary pte today is not used for anything for 64k-hpte backed ptes. It gets used the moment the pte gets backed by 4-k hptes. Till then the bits are available. And this patch makes use of that knowledge. Will add some words in the patch description towards this. Thanks, RP > > Balbir Singh. -- Ram Pai -- 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