From 8db2b1bff4b54dc01592f9e14b9dae32c341f435 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Wed, 21 May 2014 16:51:47 +0200 Subject: [PATCH 1/2] backport of fbe363 to stable 3.10.y branch MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit xen-blkfront: revoke foreign access for grants not mapped by the backend 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 Acked-by: Matt Wilson Cc: Konrad Rzeszutek Wilk Cc: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Jens Axboe --- drivers/block/xen-blkfront.c | 24 +++++++++++++++++++++--- 1 files changed, 21 insertions(+), 3 deletions(-) diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 1735b0d..cbd9f6b 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -894,9 +894,27 @@ 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 < s->req.u.rw.nr_segments; i++) { - list_add(&s->grants_used[i]->node, &info->persistent_gnts); - info->persistent_gnts_c++; + for (i = 0; i < nseg; i++) { + 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); + } } } -- 1.7.7.5 (Apple Git-26)