Re: [Xen-devel] [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
On Wed, Jun 28, 2017 at 12:43:03PM +0800, Dongli Zhang wrote:
> This patch partially reverts 3df0e50 ("xen/blkfront: pseudo support for
> multi hardware queues/rings"). The xen-blkfront queue/ring might hang due
> to grants allocation failure in the situation when gnttab_free_head is
> almost empty while many persistent grants are reserved for this queue/ring.
>
> As persistent grants management was per-queue since 73716df ("xen/blkfront:
> make persistent grants pool per-queue"), we should always allocate from
> persistent grants first.
>
> Signed-off-by: Dongli Zhang
> ---
> drivers/block/xen-blkfront.c | 17 ++---
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 3945963..d2b759f 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -713,6 +713,7 @@ static int blkif_queue_rw_req(struct request *req, struct
> blkfront_ring_info *ri
>* existing persistent grants, or if we have to get new grants,
>* as there are not sufficiently many free.
>*/
> + bool new_persistent_gnts = false;
> struct scatterlist *sg;
> int num_sg, max_grefs, num_grant;
>
> @@ -724,12 +725,13 @@ static int blkif_queue_rw_req(struct request *req,
> struct blkfront_ring_info *ri
>*/
> max_grefs += INDIRECT_GREFS(max_grefs);
>
> - /*
> - * We have to reserve 'max_grefs' grants because persistent
> - * grants are shared by all rings.
> - */
> - if (max_grefs > 0)
> - if (gnttab_alloc_grant_references(max_grefs, _head)
> < 0) {
> + /* Check if we have enough persistent grants to allocate a requests */
> + if (rinfo->persistent_gnts_c < max_grefs) {
> + new_persistent_gnts = true;
> +
> + if (gnttab_alloc_grant_references(
> + max_grefs - rinfo->persistent_gnts_c,
> + _head) < 0) {
> gnttab_request_free_callback(
> >callback,
> blkif_restart_queue_callback,
AFAICT you should also change the call to gnttab_request_free_callback
to request for max_grefs - rinfo->persistent_gnts_c. In any case the
number of persistent grants is not going to decrease now, because the
buffer is per-queue, so the only thing that can happen is that
requests complete and the number of persistent grants increase.
Roger.
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[Xen-devel] [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
This patch partially reverts 3df0e50 ("xen/blkfront: pseudo support for
multi hardware queues/rings"). The xen-blkfront queue/ring might hang due
to grants allocation failure in the situation when gnttab_free_head is
almost empty while many persistent grants are reserved for this queue/ring.
As persistent grants management was per-queue since 73716df ("xen/blkfront:
make persistent grants pool per-queue"), we should always allocate from
persistent grants first.
Signed-off-by: Dongli Zhang
---
drivers/block/xen-blkfront.c | 17 ++---
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 3945963..d2b759f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -713,6 +713,7 @@ static int blkif_queue_rw_req(struct request *req, struct
blkfront_ring_info *ri
* existing persistent grants, or if we have to get new grants,
* as there are not sufficiently many free.
*/
+ bool new_persistent_gnts = false;
struct scatterlist *sg;
int num_sg, max_grefs, num_grant;
@@ -724,12 +725,13 @@ static int blkif_queue_rw_req(struct request *req, struct
blkfront_ring_info *ri
*/
max_grefs += INDIRECT_GREFS(max_grefs);
- /*
-* We have to reserve 'max_grefs' grants because persistent
-* grants are shared by all rings.
-*/
- if (max_grefs > 0)
- if (gnttab_alloc_grant_references(max_grefs, _head)
< 0) {
+ /* Check if we have enough persistent grants to allocate a requests */
+ if (rinfo->persistent_gnts_c < max_grefs) {
+ new_persistent_gnts = true;
+
+ if (gnttab_alloc_grant_references(
+ max_grefs - rinfo->persistent_gnts_c,
+ _head) < 0) {
gnttab_request_free_callback(
>callback,
blkif_restart_queue_callback,
@@ -737,6 +739,7 @@ static int blkif_queue_rw_req(struct request *req, struct
blkfront_ring_info *ri
max_grefs);
return 1;
}
+ }
/* Fill out a communications ring structure. */
id = blkif_ring_get_request(rinfo, req, _req);
@@ -837,7 +840,7 @@ static int blkif_queue_rw_req(struct request *req, struct
blkfront_ring_info *ri
if (unlikely(require_extra_req))
rinfo->shadow[extra_id].req = *extra_ring_req;
- if (max_grefs > 0)
+ if (new_persistent_gnts)
gnttab_free_grant_references(setup.gref_head);
return 0;
--
2.7.4
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