blk-mq: scale depth and rq map appropriate if low on memory

If we are running in a kdump environment, resources are scarce.
For some SCSI setups with a huge set of shared tags, we run out
of memory allocating what the drivers is asking for. So implement
a scale back logic to reduce the tag depth for those cases, allowing
the driver to successfully load.

We should extend this to detect low memory situations, and implement
a sane fallback for those (1 queue, 64 tags, or something like that).

Tested-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 69 insertions, 19 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f9b85e83d9ba..383ea0cb1f0a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1321,6 +1321,7 @@ static void blk_mq_free_rq_map(struct blk_mq_tag_set *set,
                                 continue;
                         set->ops->exit_request(set->driver_data, tags->rqs[i],
                                                 hctx_idx, i);
+                        tags->rqs[i] = NULL;
                 }
         }
 
@@ -1354,8 +1355,9 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
 
         INIT_LIST_HEAD(&tags->page_list);
 
-        tags->rqs = kmalloc_node(set->queue_depth * sizeof(struct request *),
-                                        GFP_KERNEL, set->numa_node);
+        tags->rqs = kzalloc_node(set->queue_depth * sizeof(struct request *),
+                                 GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY,
+                                 set->numa_node);
         if (!tags->rqs) {
                 blk_mq_free_tags(tags);
                 return NULL;
@@ -1379,8 +1381,9 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
                         this_order--;
 
                 do {
-                        page = alloc_pages_node(set->numa_node, GFP_KERNEL,
-                                                this_order);
+                        page = alloc_pages_node(set->numa_node,
+                                GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY,
+                                this_order);
                         if (page)
                                 break;
                         if (!this_order--)
@@ -1404,8 +1407,10 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
                         if (set->ops->init_request) {
                                 if (set->ops->init_request(set->driver_data,
                                                 tags->rqs[i], hctx_idx, i,
-                                                set->numa_node))
+                                                set->numa_node)) {
+                                        tags->rqs[i] = NULL;
                                         goto fail;
+                                }
                         }
 
                         p += rq_size;
@@ -1416,7 +1421,6 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
         return tags;
 
 fail:
-        pr_warn("%s: failed to allocate requests\n", __func__);
         blk_mq_free_rq_map(set, tags, hctx_idx);
         return NULL;
 }
@@ -1936,6 +1940,61 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
         return NOTIFY_OK;
 }
 
+static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
+{
+        int i;
+
+        for (i = 0; i < set->nr_hw_queues; i++) {
+                set->tags[i] = blk_mq_init_rq_map(set, i);
+                if (!set->tags[i])
+                        goto out_unwind;
+        }
+
+        return 0;
+
+out_unwind:
+        while (--i >= 0)
+                blk_mq_free_rq_map(set, set->tags[i], i);
+
+        set->tags = NULL;
+        return -ENOMEM;
+}
+
+/*
+ * Allocate the request maps associated with this tag_set. Note that this
+ * may reduce the depth asked for, if memory is tight. set->queue_depth
+ * will be updated to reflect the allocated depth.
+ */
+static int blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
+{
+        unsigned int depth;
+        int err;
+
+        depth = set->queue_depth;
+        do {
+                err = __blk_mq_alloc_rq_maps(set);
+                if (!err)
+                        break;
+
+                set->queue_depth >>= 1;
+                if (set->queue_depth < set->reserved_tags + BLK_MQ_TAG_MIN) {
+                        err = -ENOMEM;
+                        break;
+                }
+        } while (set->queue_depth);
+
+        if (!set->queue_depth || err) {
+                pr_err("blk-mq: failed to allocate request map\n");
+                return -ENOMEM;
+        }
+
+        if (depth != set->queue_depth)
+                pr_info("blk-mq: reduced tag depth (%u -> %u)\n",
+                                                depth, set->queue_depth);
+
+        return 0;
+}
+
 /*
  * Alloc a tag set to be associated with one or more request queues.
  * May fail with EINVAL for various error conditions. May adjust the
@@ -1944,8 +2003,6 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
  */
 int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 {
-        int i;
-
         if (!set->nr_hw_queues)
                 return -EINVAL;
         if (!set->queue_depth)
@@ -1966,25 +2023,18 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
                                  sizeof(struct blk_mq_tags *),
                                  GFP_KERNEL, set->numa_node);
         if (!set->tags)
-                goto out;
+                return -ENOMEM;
 
-        for (i = 0; i < set->nr_hw_queues; i++) {
-                set->tags[i] = blk_mq_init_rq_map(set, i);
-                if (!set->tags[i])
-                        goto out_unwind;
-        }
+        if (blk_mq_alloc_rq_maps(set))
+                goto enomem;
 
         mutex_init(&set->tag_list_lock);
         INIT_LIST_HEAD(&set->tag_list);
 
         return 0;
-
-out_unwind:
-        while (--i >= 0)
-                blk_mq_free_rq_map(set, set->tags[i], i);
+enomem:
         kfree(set->tags);
         set->tags = NULL;
-out:
         return -ENOMEM;
 }
 EXPORT_SYMBOL(blk_mq_alloc_tag_set);