From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756010Ab2ISMDz (ORCPT ); Wed, 19 Sep 2012 08:03:55 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:40223 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751827Ab2ISMDy convert rfc822-to-8bit (ORCPT ); Wed, 19 Sep 2012 08:03:54 -0400 Message-Id: <5059D0C8020000780009C4CF@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.0 Date: Wed, 19 Sep 2012 13:03:52 +0100 From: "Jan Beulich" To: "Oliver Chick" Cc: , , Subject: Re: [Xen-devel] [PATCH] Persistent grant maps for xen blk drivers References: <1348051887-21885-1-git-send-email-oliver.chick@citrix.com> In-Reply-To: <1348051887-21885-1-git-send-email-oliver.chick@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 19.09.12 at 12:51, Oliver Chick wrote: > +/* > + * Maximum number of persistent grants that can be mapped by Dom0 for each > + * interface. This is set to be the size of the ring, as this is a limit on > + * the number of requests that can be inflight at any one time. 256 imposes > + * an overhead of 11MB of mapped kernel space per interface. > + */ > +#define BLKIF_MAX_PERS_REQUESTS_PER_DEV 256 How can this be a fixed number, especially in the context of ring size extensions? Iirc, single page rings can accommodate 64 requests, so I'd guess the number above was observed with a 4-page (order 2) ring... Jan