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From: Jens Axboe <[email protected]>
To: [email protected], [email protected]
Cc: [email protected], [email protected], [email protected],
	[email protected], Jens Axboe <[email protected]>
Subject: [PATCH 6/9] fs: add IOCB flags related to passing back dio completions
Date: Fri, 21 Jul 2023 10:16:47 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Async dio completions generally happen from hard/soft IRQ context, which
means that users like iomap may need to defer some of the completion
handling to a workqueue. This is less efficient than having the original
issuer handle it, like we do for sync IO, and it adds latency to the
completions.

Add IOCB_DIO_CALLER_COMP, which the issuer can set if it is able to
safely punt these completions to a safe context. If the dio handler is
aware of this flag, assign a callback handler in kiocb->dio_complete and
associated data io kiocb->private. The issuer will then call this
handler with that data from task context.

No functional changes in this patch.

Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
---
 include/linux/fs.h | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6867512907d6..60e2b4ecfc4d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -338,6 +338,20 @@ enum rw_hint {
 #define IOCB_NOIO		(1 << 20)
 /* can use bio alloc cache */
 #define IOCB_ALLOC_CACHE	(1 << 21)
+/*
+ * IOCB_DIO_CALLER_COMP can be set by the iocb owner, to indicate that the
+ * iocb completion can be passed back to the owner for execution from a safe
+ * context rather than needing to be punted through a workqueue.If this If this
+ * flag is set, the bio completion handling may set iocb->dio_complete to a
+ * handler function and iocb->private to context information for that handler.
+ * The issuer should call the handler with that context information from task
+ * context to complete the processing of the iocb. Note that while this
+ * provides a task context for the dio_complete() callback, it should only be
+ * used on the completion side for non-IO generating completions. It's fine to
+ * call blocking functions from this callback, but they should not wait for
+ * unrelated IO (like cache flushing, new IO generation, etc).
+ */
+#define IOCB_DIO_CALLER_COMP	(1 << 22)
 
 /* for use in trace events */
 #define TRACE_IOCB_STRINGS \
@@ -351,7 +365,8 @@ enum rw_hint {
 	{ IOCB_WRITE,		"WRITE" }, \
 	{ IOCB_WAITQ,		"WAITQ" }, \
 	{ IOCB_NOIO,		"NOIO" }, \
-	{ IOCB_ALLOC_CACHE,	"ALLOC_CACHE" }
+	{ IOCB_ALLOC_CACHE,	"ALLOC_CACHE" }, \
+	{ IOCB_DIO_CALLER_COMP,	"CALLER_COMP" }
 
 struct kiocb {
 	struct file		*ki_filp;
@@ -360,7 +375,23 @@ struct kiocb {
 	void			*private;
 	int			ki_flags;
 	u16			ki_ioprio; /* See linux/ioprio.h */
-	struct wait_page_queue	*ki_waitq; /* for async buffered IO */
+	union {
+		/*
+		 * Only used for async buffered reads, where it denotes the
+		 * page waitqueue associated with completing the read. Valid
+		 * IFF IOCB_WAITQ is set.
+		 */
+		struct wait_page_queue	*ki_waitq;
+		/*
+		 * Can be used for O_DIRECT IO, where the completion handling
+		 * is punted back to the issuer of the IO. May only be set
+		 * if IOCB_DIO_CALLER_COMP is set by the issuer, and the issuer
+		 * must then check for presence of this handler when ki_complete
+		 * is invoked. The data passed in to this handler must be
+		 * assigned to ->private when dio_complete is assigned.
+		 */
+		ssize_t (*dio_complete)(void *data);
+	};
 };
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)
-- 
2.40.1


  parent reply	other threads:[~2023-07-21 16:18 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-21 16:16 [PATCHSET v5 0/9] Improve async iomap DIO performance Jens Axboe
2023-07-21 16:16 ` [PATCH 1/9] iomap: cleanup up iomap_dio_bio_end_io() Jens Axboe
2023-07-21 16:16 ` [PATCH 2/9] iomap: add IOMAP_DIO_INLINE_COMP Jens Axboe
2023-07-21 16:16 ` [PATCH 3/9] iomap: treat a write through cache the same as FUA Jens Axboe
2023-07-21 16:25   ` Darrick J. Wong
2023-07-21 16:27     ` Jens Axboe
2023-07-21 16:47       ` Darrick J. Wong
2023-07-21 16:52         ` Jens Axboe
2023-07-21 16:16 ` [PATCH 4/9] iomap: completed polled IO inline Jens Axboe
2023-07-21 16:16 ` [PATCH 5/9] iomap: only set iocb->private for polled bio Jens Axboe
2023-07-21 16:16 ` Jens Axboe [this message]
2023-07-21 16:28   ` [PATCH 6/9] fs: add IOCB flags related to passing back dio completions Darrick J. Wong
2023-07-21 16:30     ` Jens Axboe
2023-07-21 16:43       ` Jens Axboe
2023-07-21 16:16 ` [PATCH 7/9] io_uring/rw: add write support for IOCB_DIO_CALLER_COMP Jens Axboe
2023-07-21 16:29   ` Darrick J. Wong
2023-07-21 16:16 ` [PATCH 8/9] iomap: support IOCB_DIO_CALLER_COMP Jens Axboe
2023-07-21 16:16 ` [PATCH 9/9] iomap: use an unsigned type for IOMAP_DIO_* defines Jens Axboe
2023-07-21 16:29   ` Darrick J. Wong
2023-07-24 16:36   ` Christoph Hellwig

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