[PATCH 4/5] xen-blkfront: pre-allocate pages for requests

Roger Pau Monne
2013-03-18T16:51:49Z

This prevents us from having to call alloc_page while we are preparing
the request. Since blkfront was calling alloc_page with a spinlock
held we used GFP_ATOMIC, which can fail if we are requesting a lot of
pages since it is using the emergency memory pools.

Allocating all the pages at init prevents us from having to call
alloc_page, thus preventing possible failures.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xen.org
---
Changes since RFC:
* Move page buffer initialization to setup_blkring
---
drivers/block/xen-blkfront.c | 120 +++++++++++++++++++++++++++--------------
1 files changed, 79 insertions(+), 41 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 97324cd1..c640433 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -165,6 +165,69 @@ static int add_id_to_freelist(struct blkfront_info *info,
return 0;
}

+static int fill_grant_buffer(struct blkfront_info *info, int num)
+{
+ struct page *granted_page;
+ struct grant *gnt_list_entry, *n;
+ int i = 0;
+
+ while(i < num) {
+ gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
+ if (!gnt_list_entry)
+ goto out_of_memory;
+
+ granted_page = alloc_page(GFP_NOIO);
+ if (!granted_page) {
+ kfree(gnt_list_entry);
+ goto out_of_memory;
+ }
+
+ gnt_list_entry->pfn = page_to_pfn(granted_page);
+ gnt_list_entry->gref = GRANT_INVALID_REF;
+ list_add(&gnt_list_entry->node, &info->persistent_gnts);
+ i++;
+ }
+
+ return 0;
+
+out_of_memory:
+ list_for_each_entry_safe(gnt_list_entry, n,
+ &info->persistent_gnts, node) {
+ list_del(&gnt_list_entry->node);
+ __free_page(pfn_to_page(gnt_list_entry->pfn));
+ kfree(gnt_list_entry);
+ i--;
+ }
+ BUG_ON(i != 0);
+ return -ENOMEM;
+}
+
+static struct grant *get_grant(grant_ref_t *gref_head,
+ struct blkfront_info *info)
+{
+ struct grant *gnt_list_entry;
+ unsigned long buffer_mfn;
+
+ BUG_ON(list_empty(&info->persistent_gnts));
+ gnt_list_entry = list_first_entry(&info->persistent_gnts, struct grant,
+ node);
+ list_del(&gnt_list_entry->node);
+
+ if (gnt_list_entry->gref != GRANT_INVALID_REF) {
+ info->persistent_gnts_c--;
+ return gnt_list_entry;
+ }
+
+ /* Assign a gref to this page */
+ gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
+ BUG_ON(gnt_list_entry->gref == -ENOSPC);
+ buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
+ gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
+ info->xbdev->otherend_id,
+ buffer_mfn, 0);
+ return gnt_list_entry;
+}
+
static const char *op_name(int op)
{
static const char *const names[] = {
@@ -306,7 +369,6 @@ static int blkif_queue_request(struct request *req)
*/
bool new_persistent_gnts;
grant_ref_t gref_head;
- struct page *granted_page;
struct grant *gnt_list_entry = NULL;
struct scatterlist *sg;

@@ -370,42 +432,9 @@ static int blkif_queue_request(struct request *req)
fsect = sg->offset >> 9;
lsect = fsect + (sg->length >> 9) - 1;

- if (info->persistent_gnts_c) {
- BUG_ON(list_empty(&info->persistent_gnts));
- gnt_list_entry = list_first_entry(
- &info->persistent_gnts,
- struct grant, node);
- list_del(&gnt_list_entry->node);
-
- ref = gnt_list_entry->gref;
- buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
- info->persistent_gnts_c--;
- } else {
- ref = gnttab_claim_grant_reference(&gref_head);
- BUG_ON(ref == -ENOSPC);
-
- gnt_list_entry =
- kmalloc(sizeof(struct grant),
- GFP_ATOMIC);
- if (!gnt_list_entry)
- return -ENOMEM;
-
- granted_page = alloc_page(GFP_ATOMIC);
- if (!granted_page) {
- kfree(gnt_list_entry);
- return -ENOMEM;
- }
-
- gnt_list_entry->pfn =
- page_to_pfn(granted_page);
- gnt_list_entry->gref = ref;
-
- buffer_mfn = pfn_to_mfn(page_to_pfn(
- granted_page));
- gnttab_grant_foreign_access_ref(ref,
- info->xbdev->otherend_id,
- buffer_mfn, 0);
- }
+ gnt_list_entry = get_grant(&gref_head, info);
+ ref = gnt_list_entry->gref;
+ buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);

info->shadow[id].grants_used[i] = gnt_list_entry;

@@ -803,17 +832,20 @@ static void blkif_free(struct blkfront_info *info, int suspend)
blk_stop_queue(info->rq);

/* Remove all persistent grants */
- if (info->persistent_gnts_c) {
+ if (!list_empty(&info->persistent_gnts)) {
list_for_each_entry_safe(persistent_gnt, n,
&info->persistent_gnts, node) {
list_del(&persistent_gnt->node);
- gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
+ if (persistent_gnt->gref != GRANT_INVALID_REF) {
+ gnttab_end_foreign_access(persistent_gnt->gref,
+ 0, 0UL);
+ info->persistent_gnts_c--;
+ }
__free_page(pfn_to_page(persistent_gnt->pfn));
kfree(persistent_gnt);
- info->persistent_gnts_c--;
}
- BUG_ON(info->persistent_gnts_c != 0);
}
+ BUG_ON(info->persistent_gnts_c != 0);

/* No more gnttab callback work. */
gnttab_cancel_free_callback(&info->callback);
@@ -1008,6 +1040,12 @@ static int setup_blkring(struct xenbus_device *dev,

sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);

+ /* Allocate memory for grants */
+ err = fill_grant_buffer(info, BLK_RING_SIZE *
+ BLKIF_MAX_SEGMENTS_PER_REQUEST);
+ if (err)
+ goto fail;
+
err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
if (err < 0) {
free_page((unsigned long)sring);
--
1.7.7.5 (Apple Git-26)