block: make blkcg_punt_bio_submit optional

Guard all the code to punt bios to a per-cgroup submission helper by a
new CONFIG_BLK_CGROUP_PUNT_BIO symbol that is selected by btrfs.
This way non-btrfs kernel builds don't need to have this code.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/block/Kconfig b/block/Kconfig
index 941b2dc..69ccf74 100644 (file)
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -41,6 +41,9 @@ config BLK_RQ_ALLOC_TIME
 config BLK_CGROUP_RWSTAT
        bool
 
+config BLK_CGROUP_PUNT_BIO
+       bool
+
 config BLK_DEV_BSG_COMMON
        tristate
 

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c524eca..18c9225 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -56,7 +56,6 @@ static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
 static LIST_HEAD(all_blkcgs);          /* protected by blkcg_pol_mutex */
 
 bool blkcg_debug_stats = false;
-static struct workqueue_struct *blkcg_punt_bio_wq;
 
 #define BLKG_DESTROY_BATCH_SIZE  64
 
@@ -166,7 +165,9 @@ static void __blkg_release(struct rcu_head *rcu)
 {
        struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
 
+#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
        WARN_ON(!bio_list_empty(&blkg->async_bios));
+#endif
 
        /* release the blkcg and parent blkg refs this blkg has been holding */
        css_put(&blkg->blkcg->css);
@@ -188,6 +189,9 @@ static void blkg_release(struct percpu_ref *ref)
        call_rcu(&blkg->rcu_head, __blkg_release);
 }
 
+#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
+static struct workqueue_struct *blkcg_punt_bio_wq;
+
 static void blkg_async_bio_workfn(struct work_struct *work)
 {
        struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
@@ -214,6 +218,40 @@ static void blkg_async_bio_workfn(struct work_struct *work)
                blk_finish_plug(&plug);
 }
 
+/*
+ * When a shared kthread issues a bio for a cgroup, doing so synchronously can
+ * lead to priority inversions as the kthread can be trapped waiting for that
+ * cgroup.  Use this helper instead of submit_bio to punt the actual issuing to
+ * a dedicated per-blkcg work item to avoid such priority inversions.
+ */
+void blkcg_punt_bio_submit(struct bio *bio)
+{
+       struct blkcg_gq *blkg = bio->bi_blkg;
+
+       if (blkg->parent) {
+               spin_lock(&blkg->async_bio_lock);
+               bio_list_add(&blkg->async_bios, bio);
+               spin_unlock(&blkg->async_bio_lock);
+               queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
+       } else {
+               /* never bounce for the root cgroup */
+               submit_bio(bio);
+       }
+}
+EXPORT_SYMBOL_GPL(blkcg_punt_bio_submit);
+
+static int __init blkcg_punt_bio_init(void)
+{
+       blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
+                                           WQ_MEM_RECLAIM | WQ_FREEZABLE |
+                                           WQ_UNBOUND | WQ_SYSFS, 0);
+       if (!blkcg_punt_bio_wq)
+               return -ENOMEM;
+       return 0;
+}
+subsys_initcall(blkcg_punt_bio_init);
+#endif /* CONFIG_BLK_CGROUP_PUNT_BIO */
+
 /**
  * bio_blkcg_css - return the blkcg CSS associated with a bio
  * @bio: target bio
@@ -269,10 +307,12 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
 
        blkg->q = disk->queue;
        INIT_LIST_HEAD(&blkg->q_node);
+       blkg->blkcg = blkcg;
+#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
        spin_lock_init(&blkg->async_bio_lock);
        bio_list_init(&blkg->async_bios);
        INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
-       blkg->blkcg = blkcg;
+#endif
 
        u64_stats_init(&blkg->iostat.sync);
        for_each_possible_cpu(cpu) {
@@ -1689,28 +1729,6 @@ out_unlock:
 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
 
 /*
- * When a shared kthread issues a bio for a cgroup, doing so synchronously can
- * lead to priority inversions as the kthread can be trapped waiting for that
- * cgroup.  Use this helper instead of submit_bio to punt the actual issuing to
- * a dedicated per-blkcg work item to avoid such priority inversions.
- */
-void blkcg_punt_bio_submit(struct bio *bio)
-{
-       struct blkcg_gq *blkg = bio->bi_blkg;
-
-       if (blkg->parent) {
-               spin_lock(&blkg->async_bio_lock);
-               bio_list_add(&blkg->async_bios, bio);
-               spin_unlock(&blkg->async_bio_lock);
-               queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
-       } else {
-               /* never bounce for the root cgroup */
-               submit_bio(bio);
-       }
-}
-EXPORT_SYMBOL_GPL(blkcg_punt_bio_submit);
-
-/*
  * Scale the accumulated delay based on how long it has been since we updated
  * the delay.  We only call this when we are adding delay, in case it's been a
  * while since we added delay, and when we are checking to see if we need to
@@ -2088,16 +2106,5 @@ bool blk_cgroup_congested(void)
        return ret;
 }
 
-static int __init blkcg_init(void)
-{
-       blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
-                                           WQ_MEM_RECLAIM | WQ_FREEZABLE |
-                                           WQ_UNBOUND | WQ_SYSFS, 0);
-       if (!blkcg_punt_bio_wq)
-               return -ENOMEM;
-       return 0;
-}
-subsys_initcall(blkcg_init);
-
 module_param(blkcg_debug_stats, bool, 0644);
 MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 64758ab..e98d2c1 100644 (file)
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -72,9 +72,10 @@ struct blkcg_gq {
        struct blkg_iostat_set          iostat;
 
        struct blkg_policy_data         *pd[BLKCG_MAX_POLS];
-
+#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
        spinlock_t                      async_bio_lock;
        struct bio_list                 async_bios;
+#endif
        union {
                struct work_struct      async_bio_work;
                struct work_struct      free_work;

diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 37b6bab..66fa9ab 100644 (file)
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -2,6 +2,7 @@
 
 config BTRFS_FS
        tristate "Btrfs filesystem support"
+       select BLK_CGROUP_PUNT_BIO
        select CRYPTO
        select CRYPTO_CRC32C
        select LIBCRC32C