From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751156Ab3HAGgD (ORCPT ); Thu, 1 Aug 2013 02:36:03 -0400 Received: from smtp-fw-2101.amazon.com ([72.21.196.25]:6995 "EHLO smtp-fw-2101.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750742Ab3HAGgB (ORCPT ); Thu, 1 Aug 2013 02:36:01 -0400 X-IronPort-AV: E=Sophos;i="4.89,791,1367971200"; d="scan'208";a="587673798" Date: Wed, 31 Jul 2013 23:35:11 -0700 From: Matt Wilson To: Roger Pau Monne CC: , , David Vrabel Subject: Re: [PATCH 3/3] xen-blkfront: revoke foreign access for grants not mapped by the backend Message-ID: <20130801063509.GF4239@u109add4315675089e695.ant.amazon.com> References: <1375282844-4314-1-git-send-email-roger.pau@citrix.com> <1375282844-4314-4-git-send-email-roger.pau@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1375282844-4314-4-git-send-email-roger.pau@citrix.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 31, 2013 at 05:00:44PM +0200, 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 Acked-by: Matt Wilson > Cc: Konrad Rzeszutek Wilk > Cc: David Vrabel > --- > drivers/block/xen-blkfront.c | 33 +++++++++++++++++++++++++++++---- > 1 files changed, 29 insertions(+), 4 deletions(-) > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > index 187a437..bc9fc7d 100644 > --- 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); > + } > } > if (s->req.operation == BLKIF_OP_INDIRECT) { > for (i = 0; i < INDIRECT_GREFS(nseg); i++) { > - list_add(&s->indirect_grants[i]->node, &info->persistent_gnts); > - info->persistent_gnts_c++; > + if (gnttab_query_foreign_access(s->indirect_grants[i]->gref)) { > + list_add(&s->indirect_grants[i]->node, &info->persistent_gnts); > + info->persistent_gnts_c++; > + } else { > + gnttab_end_foreign_access(s->indirect_grants[i]->gref, 0, 0UL); > + s->indirect_grants[i]->gref = GRANT_INVALID_REF; > + list_add_tail(&s->indirect_grants[i]->node, > + &info->persistent_gnts); > + } > } > } > }