direct-io: Implement generic deferred AIO completions
Add support to the core direct-io code to defer AIO completions to user
context using a workqueue. This replaces opencoded and less efficient
code in XFS and ext4 (we save a memory allocation for each direct IO)
and will be needed to properly support O_(D)SYNC for AIO.
The communication between the filesystem and the direct I/O code requires
a new buffer head flag, which is a bit ugly but not avoidable until the
direct I/O code stops abusing the buffer_head structure for communicating
with the filesystems.
Currently this creates a per-superblock unbound workqueue for these
completions, which is taken from an earlier patch by Jan Kara. I'm
not really convinced about this use and would prefer a "normal" global
workqueue with a high concurrency limit, but this needs further discussion.
JK: Fixed ext4 part, dynamic allocation of the workqueue.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 7ab90f5..8b31b9f 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -127,6 +127,7 @@
spinlock_t bio_lock; /* protects BIO fields below */
int page_errors; /* errno from get_user_pages() */
int is_async; /* is IO async ? */
+ bool defer_completion; /* defer AIO completion to workqueue? */
int io_error; /* IO error in completion path */
unsigned long refcount; /* direct_io_worker() and bios */
struct bio *bio_list; /* singly linked via bi_private */
@@ -141,7 +142,10 @@
* allocation time. Don't add new fields after pages[] unless you
* wish that they not be zeroed.
*/
- struct page *pages[DIO_PAGES]; /* page buffer */
+ union {
+ struct page *pages[DIO_PAGES]; /* page buffer */
+ struct work_struct complete_work;/* deferred AIO completion */
+ };
} ____cacheline_aligned_in_smp;
static struct kmem_cache *dio_cache __read_mostly;
@@ -221,16 +225,16 @@
* dio_complete() - called when all DIO BIO I/O has been completed
* @offset: the byte offset in the file of the completed operation
*
- * This releases locks as dictated by the locking type, lets interested parties
- * know that a DIO operation has completed, and calculates the resulting return
- * code for the operation.
+ * This drops i_dio_count, lets interested parties know that a DIO operation
+ * has completed, and calculates the resulting return code for the operation.
*
* It lets the filesystem know if it registered an interest earlier via
* get_block. Pass the private field of the map buffer_head so that
* filesystems can use it to hold additional state between get_block calls and
* dio_complete.
*/
-static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async)
+static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
+ bool is_async)
{
ssize_t transferred = 0;
@@ -258,19 +262,26 @@
if (ret == 0)
ret = transferred;
- if (dio->end_io && dio->result) {
- dio->end_io(dio->iocb, offset, transferred,
- dio->private, ret, is_async);
- } else {
- inode_dio_done(dio->inode);
- if (is_async)
- aio_complete(dio->iocb, ret, 0);
- }
+ if (dio->end_io && dio->result)
+ dio->end_io(dio->iocb, offset, transferred, dio->private);
+ inode_dio_done(dio->inode);
+ if (is_async)
+ aio_complete(dio->iocb, ret, 0);
+
+ kmem_cache_free(dio_cache, dio);
return ret;
}
+static void dio_aio_complete_work(struct work_struct *work)
+{
+ struct dio *dio = container_of(work, struct dio, complete_work);
+
+ dio_complete(dio, dio->iocb->ki_pos, 0, true);
+}
+
static int dio_bio_complete(struct dio *dio, struct bio *bio);
+
/*
* Asynchronous IO callback.
*/
@@ -290,8 +301,13 @@
spin_unlock_irqrestore(&dio->bio_lock, flags);
if (remaining == 0) {
- dio_complete(dio, dio->iocb->ki_pos, 0, true);
- kmem_cache_free(dio_cache, dio);
+ if (dio->result && dio->defer_completion) {
+ INIT_WORK(&dio->complete_work, dio_aio_complete_work);
+ queue_work(dio->inode->i_sb->s_dio_done_wq,
+ &dio->complete_work);
+ } else {
+ dio_complete(dio, dio->iocb->ki_pos, 0, true);
+ }
}
}
@@ -511,6 +527,41 @@
}
/*
+ * Create workqueue for deferred direct IO completions. We allocate the
+ * workqueue when it's first needed. This avoids creating workqueue for
+ * filesystems that don't need it and also allows us to create the workqueue
+ * late enough so the we can include s_id in the name of the workqueue.
+ */
+static int sb_init_dio_done_wq(struct super_block *sb)
+{
+ struct workqueue_struct *wq = alloc_workqueue("dio/%s",
+ WQ_MEM_RECLAIM, 0,
+ sb->s_id);
+ if (!wq)
+ return -ENOMEM;
+ /*
+ * This has to be atomic as more DIOs can race to create the workqueue
+ */
+ cmpxchg(&sb->s_dio_done_wq, NULL, wq);
+ /* Someone created workqueue before us? Free ours... */
+ if (wq != sb->s_dio_done_wq)
+ destroy_workqueue(wq);
+ return 0;
+}
+
+static int dio_set_defer_completion(struct dio *dio)
+{
+ struct super_block *sb = dio->inode->i_sb;
+
+ if (dio->defer_completion)
+ return 0;
+ dio->defer_completion = true;
+ if (!sb->s_dio_done_wq)
+ return sb_init_dio_done_wq(sb);
+ return 0;
+}
+
+/*
* Call into the fs to map some more disk blocks. We record the current number
* of available blocks at sdio->blocks_available. These are in units of the
* fs blocksize, (1 << inode->i_blkbits).
@@ -581,6 +632,9 @@
/* Store for completion */
dio->private = map_bh->b_private;
+
+ if (ret == 0 && buffer_defer_completion(map_bh))
+ ret = dio_set_defer_completion(dio);
}
return ret;
}
@@ -1269,7 +1323,6 @@
if (drop_refcount(dio) == 0) {
retval = dio_complete(dio, offset, retval, false);
- kmem_cache_free(dio_cache, dio);
} else
BUG_ON(retval != -EIOCBQUEUED);