Revert "Pre-allocate vdev I/O buffers"

Commit 86dd0fd added preallocated I/O buffers.  This is no longer
required after the recent kmem changes designed to make our memory
allocation interfaces behave more like those found on Illumos.  A
deadlock in this situation is no longer possible.

However, these allocations still have the potential to be expensive.
So a potential future optimization might be to perform then KM_NOSLEEP
so that they either succeed of fail quicky.  Either case is acceptable
here because we can safely abort the aggregation.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/vdev_impl.h

@@ -50,7 +50,6 @@ extern "C" {
  * Forward declarations that lots of things need.
  */
 typedef struct vdev_queue vdev_queue_t;
-typedef struct vdev_io vdev_io_t;
 typedef struct vdev_cache vdev_cache_t;
 typedef struct vdev_cache_entry vdev_cache_entry_t;
 
@@ -117,16 +116,10 @@ struct vdev_queue {
 	uint64_t	vq_last_offset;
 	hrtime_t	vq_io_complete_ts; /* time last i/o completed */
 	hrtime_t	vq_io_delta_ts;
-	list_t		vq_io_list;
 	zio_t		vq_io_search; /* used as local for stack reduction */
 	kmutex_t	vq_lock;
 };
 
-struct vdev_io {
-	char		vi_buffer[SPA_MAXBLOCKSIZE]; /* Must be first */
-	list_node_t	vi_node;
-};
-
 /*
  * Virtual device descriptor
  */

include/sys/zio.h

@@ -522,8 +522,6 @@ extern void *zio_buf_alloc(size_t size);
 extern void zio_buf_free(void *buf, size_t size);
 extern void *zio_data_buf_alloc(size_t size);
 extern void zio_data_buf_free(void *buf, size_t size);
-extern void *zio_vdev_alloc(void);
-extern void zio_vdev_free(void *buf);
 
 extern void zio_resubmit_stage_async(void *);
 

module/zfs/vdev_queue.c

@@ -328,9 +328,7 @@ void
 vdev_queue_init(vdev_t *vd)
 {
 	vdev_queue_t *vq = &vd->vdev_queue;
-	int max_active_sum;
 	zio_priority_t p;
-	int i;
 
 	mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);
 	vq->vq_vdev = vd;
@@ -352,39 +350,18 @@ vdev_queue_init(vdev_t *vd)
 		    vdev_queue_offset_compare,
 		    sizeof (zio_t), offsetof(struct zio, io_queue_node));
 	}
-
-	/*
-	 * A list of buffers which can be used for aggregate I/O, this
-	 * avoids the need to allocate them on demand when memory is low.
-	 */
-	list_create(&vq->vq_io_list, sizeof (vdev_io_t),
-	    offsetof(vdev_io_t, vi_node));
-
-	max_active_sum = zfs_vdev_sync_read_max_active +
-	    zfs_vdev_sync_write_max_active + zfs_vdev_async_read_max_active +
-	    zfs_vdev_async_write_max_active + zfs_vdev_scrub_max_active;
-	for (i = 0; i < max_active_sum; i++)
-		list_insert_tail(&vq->vq_io_list, zio_vdev_alloc());
 }
 
 void
 vdev_queue_fini(vdev_t *vd)
 {
 	vdev_queue_t *vq = &vd->vdev_queue;
-	vdev_io_t *vi;
 	zio_priority_t p;
 
 	for (p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++)
 		avl_destroy(&vq->vq_class[p].vqc_queued_tree);
 	avl_destroy(&vq->vq_active_tree);
 
-	while ((vi = list_head(&vq->vq_io_list)) != NULL) {
-		list_remove(&vq->vq_io_list, vi);
-		zio_vdev_free(vi);
-	}
-
-	list_destroy(&vq->vq_io_list);
-
 	mutex_destroy(&vq->vq_lock);
 }
 
@@ -468,9 +445,6 @@ vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
 static void
 vdev_queue_agg_io_done(zio_t *aio)
 {
-	vdev_queue_t *vq = &aio->io_vd->vdev_queue;
-	vdev_io_t *vi = aio->io_data;
-
 	if (aio->io_type == ZIO_TYPE_READ) {
 		zio_t *pio;
 		while ((pio = zio_walk_parents(aio)) != NULL) {
@@ -479,9 +453,7 @@ vdev_queue_agg_io_done(zio_t *aio)
 		}
 	}
 
-	mutex_enter(&vq->vq_lock);
+	zio_buf_free(aio->io_data, aio->io_size);
-	list_insert_tail(&vq->vq_io_list, vi);
-	mutex_exit(&vq->vq_lock);
 }
 
 /*
@@ -496,7 +468,6 @@ vdev_queue_agg_io_done(zio_t *aio)
 static zio_t *
 vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 {
-	vdev_io_t *vi;
 	zio_t *first, *last, *aio, *dio, *mandatory, *nio;
 	uint64_t maxgap = 0;
 	uint64_t size;
@@ -529,12 +500,6 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	if (zio->io_type == ZIO_TYPE_READ)
 		maxgap = zfs_vdev_read_gap_limit;
 
-	vi = list_head(&vq->vq_io_list);
-	if (vi == NULL) {
-		vi = zio_vdev_alloc();
-		list_insert_head(&vq->vq_io_list, vi);
-	}
-
 	/*
 	 * We can aggregate I/Os that are sufficiently adjacent and of
 	 * the same flavor, as expressed by the AGG_INHERIT flags.
@@ -622,13 +587,11 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	if (first == last)
 		return (NULL);
 
-	ASSERT(vi != NULL);
-
 	size = IO_SPAN(first, last);
 	ASSERT3U(size, <=, zfs_vdev_aggregation_limit);
 
 	aio = zio_vdev_delegated_io(first->io_vd, first->io_offset,
-	    vi, size, first->io_type, zio->io_priority,
+	    zio_buf_alloc(size), size, first->io_type, zio->io_priority,
 	    flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
 	    vdev_queue_agg_io_done, NULL);
 	aio->io_timestamp = first->io_timestamp;
@@ -655,8 +618,6 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 		zio_execute(dio);
 	} while (dio != last);
 
-	list_remove(&vq->vq_io_list, vi);
-
 	return (aio);
 }
 

module/zfs/zio.c

@@ -55,7 +55,6 @@ const char *zio_type_name[ZIO_TYPES] = {
  */
 kmem_cache_t *zio_cache;
 kmem_cache_t *zio_link_cache;
-kmem_cache_t *zio_vdev_cache;
 kmem_cache_t *zio_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
 kmem_cache_t *zio_data_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
 int zio_bulk_flags = 0;
@@ -132,8 +131,6 @@ zio_init(void)
 	    zio_cons, zio_dest, NULL, NULL, NULL, 0);
 	zio_link_cache = kmem_cache_create("zio_link_cache",
 	    sizeof (zio_link_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
-	zio_vdev_cache = kmem_cache_create("zio_vdev_cache", sizeof (vdev_io_t),
-	    PAGESIZE, NULL, NULL, NULL, NULL, NULL, 0);
 
 	/*
 	 * For small buffers, we want a cache for each multiple of
@@ -218,7 +215,6 @@ zio_fini(void)
 		zio_data_buf_cache[c] = NULL;
 	}
 
-	kmem_cache_destroy(zio_vdev_cache);
 	kmem_cache_destroy(zio_link_cache);
 	kmem_cache_destroy(zio_cache);
 
@@ -285,24 +281,6 @@ zio_data_buf_free(void *buf, size_t size)
 	kmem_cache_free(zio_data_buf_cache[c], buf);
 }
 
-/*
- * Dedicated I/O buffers to ensure that memory fragmentation never prevents
- * or significantly delays the issuing of a zio.   These buffers are used
- * to aggregate I/O and could be used for raidz stripes.
- */
-void *
-zio_vdev_alloc(void)
-{
-	return (kmem_cache_alloc(zio_vdev_cache, KM_PUSHPAGE));
-}
-
-void
-zio_vdev_free(void *buf)
-{
-	kmem_cache_free(zio_vdev_cache, buf);
-
-}
-
 /*
  * ==========================================================================
  * Push and pop I/O transform buffers