* [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
@ 2017-06-28 4:43 Dongli Zhang
2017-06-28 8:34 ` Roger Pau Monné
2017-06-28 8:34 ` Roger Pau Monné
0 siblings, 2 replies; 4+ messages in thread
From: Dongli Zhang @ 2017-06-28 4:43 UTC (permalink / raw)
To: xen-devel, linux-kernel; +Cc: konrad.wilk, roger.pau, boris.ostrovsky, jgross
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 <dongli.zhang@oracle.com>
---
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, &setup.gref_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,
+ &setup.gref_head) < 0) {
gnttab_request_free_callback(
&rinfo->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, &ring_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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
2017-06-28 4:43 [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants Dongli Zhang
2017-06-28 8:34 ` Roger Pau Monné
@ 2017-06-28 8:34 ` Roger Pau Monné
1 sibling, 0 replies; 4+ messages in thread
From: Roger Pau Monné @ 2017-06-28 8:34 UTC (permalink / raw)
To: Dongli Zhang
Cc: xen-devel, linux-kernel, konrad.wilk, boris.ostrovsky, jgross
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 <dongli.zhang@oracle.com>
> ---
> 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, &setup.gref_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,
> + &setup.gref_head) < 0) {
> gnttab_request_free_callback(
> &rinfo->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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
2017-06-28 4:43 [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants Dongli Zhang
@ 2017-06-28 8:34 ` Roger Pau Monné
2017-06-28 8:34 ` Roger Pau Monné
1 sibling, 0 replies; 4+ messages in thread
From: Roger Pau Monné @ 2017-06-28 8:34 UTC (permalink / raw)
To: Dongli Zhang; +Cc: jgross, xen-devel, boris.ostrovsky, linux-kernel
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 <dongli.zhang@oracle.com>
> ---
> 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, &setup.gref_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,
> + &setup.gref_head) < 0) {
> gnttab_request_free_callback(
> &rinfo->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.
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH 1/1] xen/blkfront: always allocate grants first from per-queue persistent grants
@ 2017-06-28 4:43 Dongli Zhang
0 siblings, 0 replies; 4+ messages in thread
From: Dongli Zhang @ 2017-06-28 4:43 UTC (permalink / raw)
To: xen-devel, linux-kernel; +Cc: jgross, boris.ostrovsky, roger.pau
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 <dongli.zhang@oracle.com>
---
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, &setup.gref_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,
+ &setup.gref_head) < 0) {
gnttab_request_free_callback(
&rinfo->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, &ring_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
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel
^ permalink raw reply related [flat|nested] 4+ messages in thread
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2017-06-28 8:34 ` Roger Pau Monné
2017-06-28 8:34 ` Roger Pau Monné
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