From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43383) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1chIUK-0001pr-Jo for qemu-devel@nongnu.org; Fri, 24 Feb 2017 11:12:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1chIUJ-0005tk-Lw for qemu-devel@nongnu.org; Fri, 24 Feb 2017 11:12:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43708) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1chIUJ-0005te-Fj for qemu-devel@nongnu.org; Fri, 24 Feb 2017 11:12:55 -0500 Received: from smtp.corp.redhat.com (int-mx16.intmail.prod.int.phx2.redhat.com [10.5.11.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ACAD8C05B1D4 for ; Fri, 24 Feb 2017 16:12:55 +0000 (UTC) References: <20170206173306.20603-1-dgilbert@redhat.com> <20170206173306.20603-17-dgilbert@redhat.com> From: Laurent Vivier Message-ID: <2cc45dbb-8e49-a753-53a8-0c3a2ff18a05@redhat.com> Date: Fri, 24 Feb 2017 17:12:52 +0100 MIME-Version: 1.0 In-Reply-To: <20170206173306.20603-17-dgilbert@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit 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)" , qemu-devel@nongnu.org, quintela@redhat.com Cc: aarcange@redhat.com On 06/02/2017 18:33, 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: Laurent Vivier