From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45528) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1canAQ-0004AF-5Q for qemu-devel@nongnu.org; Mon, 06 Feb 2017 12:33:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1canAO-0006Uj-5I for qemu-devel@nongnu.org; Mon, 06 Feb 2017 12:33:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37798) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1canAO-0006TT-0B for qemu-devel@nongnu.org; Mon, 06 Feb 2017 12:33:28 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (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 308927E9EF for ; Mon, 6 Feb 2017 17:33:28 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" Date: Mon, 6 Feb 2017 17:33:06 +0000 Message-Id: <20170206173306.20603-17-dgilbert@redhat.com> In-Reply-To: <20170206173306.20603-1-dgilbert@redhat.com> References: <20170206173306.20603-1-dgilbert@redhat.com> Subject: [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: qemu-devel@nongnu.org, quintela@redhat.com Cc: aarcange@redhat.com 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. -- 2.9.3