Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754513Ab3HAKKT (ORCPT ); Thu, 1 Aug 2013 06:10:19 -0400 Received: from smtp.citrix.com ([66.165.176.89]:27992 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039Ab3HAKKR (ORCPT ); Thu, 1 Aug 2013 06:10:17 -0400 X-IronPort-AV: E=Sophos;i="4.89,793,1367971200"; d="scan'208";a="40707493" Message-ID: <51FA3407.7050106@citrix.com> Date: Thu, 1 Aug 2013 11:10:15 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Roger Pau Monne CC: , , David Vrabel Subject: Re: [Xen-devel] [PATCH 3/3] xen-blkfront: revoke foreign access for grants not mapped by the backend References: <1375282844-4314-1-git-send-email-roger.pau@citrix.com> <1375282844-4314-4-git-send-email-roger.pau@citrix.com> In-Reply-To: <1375282844-4314-4-git-send-email-roger.pau@citrix.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.2.76] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2683 Lines: 67 On 31/07/13 16:00, Roger Pau Monne wrote: > There's no need to keep the foreign access in a grant if it is not > persistently mapped by the backend. This allows us to free grants that > are not mapped by the backend, thus preventing blkfront from hoarding > all grants. > > The main effect of this is that blkfront will only persistently map > the same grants as the backend, and it will always try to use grants > that are already mapped by the backend. Also the number of persistent > grants in blkfront is the same as in blkback (and is controlled by the > value in blkback). > > Signed-off-by: Roger Pau Monné Reviewed-by: David Vrabel But please see the documentation updates needed below. > --- a/drivers/block/xen-blkfront.c > +++ b/drivers/block/xen-blkfront.c > @@ -1016,13 +1016,38 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info, > } > /* Add the persistent grant into the list of free grants */ > for (i = 0; i < nseg; i++) { > - list_add(&s->grants_used[i]->node, &info->persistent_gnts); > - info->persistent_gnts_c++; > + if (gnttab_query_foreign_access(s->grants_used[i]->gref)) { > + /* > + * If the grant is still mapped by the backend (the > + * backend has chosen to make this grant persistent) > + * we add it at the head of the list, so it will be > + * reused first. > + */ > + list_add(&s->grants_used[i]->node, &info->persistent_gnts); > + info->persistent_gnts_c++; > + } else { > + /* > + * If the grant is not mapped by the backend we end the > + * foreign access and add it to the tail of the list, > + * so it will not be picked again unless we run out of > + * persistent grants. > + */ > + gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL); > + s->grants_used[i]->gref = GRANT_INVALID_REF; > + list_add_tail(&s->grants_used[i]->node, &info->persistent_gnts); > + } Because you only reclaim grants when a request is completed, can you add text similar to the following to xen/include/public/io/blkif.h (and the Linux copy). feature-persistent: ... When the backend driver needs to unmap a persistent grant it should do so prior to completing a request that used that grant reference. If a persistent grant is unmapped at any other time, the frontend driver may not notice and may be unable to reclaim the grant reference. Thanks. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/