From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56799) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1chFsw-0000g3-Od for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:26:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1chFst-0003se-IN for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:26:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43402) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1chFst-0003sT-D6 for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:26:07 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AEBD0C04B93B for ; Fri, 24 Feb 2017 13:26:06 +0000 (UTC) From: Juan Quintela In-Reply-To: <20170206173306.20603-17-dgilbert@redhat.com> (David Alan Gilbert's message of "Mon, 6 Feb 2017 17:33:06 +0000") References: <20170206173306.20603-1-dgilbert@redhat.com> <20170206173306.20603-17-dgilbert@redhat.com> Reply-To: quintela@redhat.com Date: Fri, 24 Feb 2017 14:25:56 +0100 Message-ID: <871sunk9ej.fsf@emacs.mitica> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v2 16/16] postcopy: Add doc about hugepages and postcopy List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert (git)" Cc: qemu-devel@nongnu.org, aarcange@redhat.com "Dr. David Alan Gilbert (git)" wrote: > From: "Dr. David Alan Gilbert" > > Signed-off-by: Dr. David Alan Gilbert > --- > docs/migration.txt | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/docs/migration.txt b/docs/migration.txt > index 6503c17..b462ead 100644 > --- a/docs/migration.txt > +++ b/docs/migration.txt > @@ -482,3 +482,16 @@ request for a page that has already been sent is > ignored. Duplicate requests > such as this can happen as a page is sent at about the same time the > destination accesses it. > > +=== Postcopy with hugepages === > + > +Postcopy now works with hugetlbfs backed memory: > + a) The linux kernel on the destination must support userfault on hugepages. > + b) The huge-page configuration on the source and destination VMs must be > + identical; i.e. RAMBlocks on both sides must use the same page size. > + c) Note that -mem-path /dev/hugepages will fall back to allocating normal > + RAM if it doesn't have enough hugepages, triggering (b) to fail. > + Using -mem-prealloc enforces the allocation using hugepages. > + d) Care should be taken with the size of hugepage used; postcopy with 2MB > + hugepages works well, however 1GB hugepages are likely to be problematic > + since it takes ~1 second to transfer a 1GB hugepage across a 10Gbps link, > + and until the full page is transferred the destination thread is blocked. Reviewed-by: Juan Quintela