From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:36708)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <aneesh.kumar@linux.vnet.ibm.com>) id 1a3iZI-00029f-4M
	for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:53:57 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <aneesh.kumar@linux.vnet.ibm.com>) id 1a3iZE-00056n-S7
	for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:53:56 -0500
Received: from e28smtp08.in.ibm.com ([122.248.162.8]:39618)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <aneesh.kumar@linux.vnet.ibm.com>) id 1a3iZE-00056M-7V
	for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:53:52 -0500
Received: from localhost
	by e28smtp08.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use
	Only! Violators will be prosecuted
	for <qemu-devel@nongnu.org> from <aneesh.kumar@linux.vnet.ibm.com>;
	Tue, 1 Dec 2015 16:23:49 +0530
Received: from d28relay04.in.ibm.com (d28relay04.in.ibm.com [9.184.220.61])
	by d28dlp02.in.ibm.com (Postfix) with ESMTP id E2D6B3940060
	for <qemu-devel@nongnu.org>; Tue,  1 Dec 2015 16:23:46 +0530 (IST)
Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67])
	by d28relay04.in.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id
	tB1ArIkO8061366
	for <qemu-devel@nongnu.org>; Tue, 1 Dec 2015 16:23:18 +0530
Received: from d28av05.in.ibm.com (localhost [127.0.0.1])
	by d28av05.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id
	tB1ArGkW031636
	for <qemu-devel@nongnu.org>; Tue, 1 Dec 2015 16:23:17 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
In-Reply-To: <20151130185328-mutt-send-email-mst@redhat.com>
References: <20151130105044.12269.21261.stgit@bahia.huguette.org>
	<20151130150353-mutt-send-email-mst@redhat.com>
	<20151130144631.4736280b@bahia.local>
	<20151130185328-mutt-send-email-mst@redhat.com>
Date: Tue, 01 Dec 2015 16:23:11 +0530
Message-ID: <878u5eqw2w.fsf@linux.vnet.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [Qemu-devel] [PATCH] mmap-alloc: use same backend for
	all	mappings
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Michael S. Tsirkin" <mst@redhat.com>, Greg Kurz <gkurz@linux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org

"Michael S. Tsirkin" <mst@redhat.com> writes:

> On Mon, Nov 30, 2015 at 02:46:31PM +0100, Greg Kurz wrote:
>> On Mon, 30 Nov 2015 15:06:33 +0200
>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>> 


....
>> 
>> On ppc64, the address space is divided in 256MB-sized segments where all pages
>> have the same size. This is a hw limitation IIUC. I don't know if it can be
>> fixed and I'll let Ben comment on it.
>
> But it's anonymous memory with PROT_NONE.  There should be no pages there:
> just a chunk of virtual memory reserved.
>

ppc64 use page size (called as base page size) to find the hash slot in
which we find the virtual address to real address translation. All the
pages in a segment should have same base page size. Hugetlb pages have a
base page size of 16M whereas a regular linux page have 64K. mmap will
fail to map a hugetlb mapping in a segment that already have regular
pages mapped.

-aneesh