[PATCH v4 37/48] xfs: dynamically allocate the xfs-buf shrinker

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the xfs-buf shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct xfs_buftarg.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 fs/xfs/xfs_buf.c | 25 ++++++++++++++-----------
 fs/xfs/xfs_buf.h |  2 +-
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 15d1e5a7c2d3..715730fc91cb 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1906,8 +1906,7 @@ xfs_buftarg_shrink_scan(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_buftarg	*btp = container_of(shrink,
-					struct xfs_buftarg, bt_shrinker);
+	struct xfs_buftarg	*btp = shrink->private_data;
 	LIST_HEAD(dispose);
 	unsigned long		freed;
 
@@ -1929,8 +1928,7 @@ xfs_buftarg_shrink_count(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_buftarg	*btp = container_of(shrink,
-					struct xfs_buftarg, bt_shrinker);
+	struct xfs_buftarg	*btp = shrink->private_data;
 	return list_lru_shrink_count(&btp->bt_lru, sc);
 }
 
@@ -1938,7 +1936,7 @@ void
 xfs_free_buftarg(
 	struct xfs_buftarg	*btp)
 {
-	unregister_shrinker(&btp->bt_shrinker);
+	shrinker_free(btp->bt_shrinker);
 	ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
 	percpu_counter_destroy(&btp->bt_io_count);
 	list_lru_destroy(&btp->bt_lru);
@@ -2021,13 +2019,18 @@ xfs_alloc_buftarg(
 	if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
 		goto error_lru;
 
-	btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
-	btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
-	btp->bt_shrinker.seeks = DEFAULT_SEEKS;
-	btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
-	if (register_shrinker(&btp->bt_shrinker, "xfs-buf:%s",
-			      mp->m_super->s_id))
+	btp->bt_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "xfs-buf:%s",
+					  mp->m_super->s_id);
+	if (!btp->bt_shrinker)
 		goto error_pcpu;
+
+	btp->bt_shrinker->count_objects = xfs_buftarg_shrink_count;
+	btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
+	btp->bt_shrinker->seeks = DEFAULT_SEEKS;
+	btp->bt_shrinker->private_data = btp;
+
+	shrinker_register(btp->bt_shrinker);
+
 	return btp;
 
 error_pcpu:
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 549c60942208..4e6969a675f7 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -102,7 +102,7 @@ typedef struct xfs_buftarg {
 	size_t			bt_logical_sectormask;
 
 	/* LRU control structures */
-	struct shrinker		bt_shrinker;
+	struct shrinker		*bt_shrinker;
 	struct list_lru		bt_lru;
 
 	struct percpu_counter	bt_io_count;
-- 
2.30.2