public inbox for [email protected]
 help / color / mirror / Atom feed
From: Jens Axboe <[email protected]>
To: [email protected], [email protected]
Cc: [email protected], [email protected], [email protected],
	Jens Axboe <[email protected]>
Subject: [PATCH 2/5] fs: add IOCB flags related to passing back dio completions
Date: Tue, 18 Jul 2023 13:49:17 -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_DEFER, 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.

Signed-off-by: Jens Axboe <[email protected]>
---
 include/linux/fs.h | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6867512907d6..115382f66d79 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -338,6 +338,16 @@ enum rw_hint {
 #define IOCB_NOIO		(1 << 20)
 /* can use bio alloc cache */
 #define IOCB_ALLOC_CACHE	(1 << 21)
+/*
+ * IOCB_DIO_DEFER 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
+ * flag is set, the completion handling may set iocb->dio_complete to a
+ * handler, which the issuer will then call from task context to complete
+ * the processing of the iocb. iocb->private should then also be set to
+ * the argument being passed to this handler.
+ */
+#define IOCB_DIO_DEFER		(1 << 22)
 
 /* for use in trace events */
 #define TRACE_IOCB_STRINGS \
@@ -351,7 +361,8 @@ enum rw_hint {
 	{ IOCB_WRITE,		"WRITE" }, \
 	{ IOCB_WAITQ,		"WAITQ" }, \
 	{ IOCB_NOIO,		"NOIO" }, \
-	{ IOCB_ALLOC_CACHE,	"ALLOC_CACHE" }
+	{ IOCB_ALLOC_CACHE,	"ALLOC_CACHE" }, \
+	{ IOCB_DIO_DEFER,	"DIO_DEFER" }
 
 struct kiocb {
 	struct file		*ki_filp;
@@ -360,7 +371,22 @@ 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_DEFER is set by the issuer, and the issuer must
+		 * then check for presence of this handler when ki_complete is
+		 * invoked.
+		 */
+		ssize_t (*dio_complete)(void *data);
+	};
 };
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)
-- 
2.40.1


  parent reply	other threads:[~2023-07-18 19:49 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-18 19:49 [PATCHSET v2 0/5] Improve async iomap DIO performance Jens Axboe
2023-07-18 19:49 ` [PATCH] io_uring: Use io_schedule* in cqring wait Jens Axboe
2023-07-18 19:50   ` Jens Axboe
2023-07-18 19:49 ` [PATCH 1/5] iomap: simplify logic for when a dio can get completed inline Jens Axboe
2023-07-18 22:56   ` Dave Chinner
2023-07-19 15:23     ` Jens Axboe
2023-07-18 19:49 ` Jens Axboe [this message]
2023-07-18 19:49 ` [PATCH 3/5] io_uring/rw: add write support for IOCB_DIO_DEFER Jens Axboe
2023-07-18 19:49 ` [PATCH 4/5] iomap: add local 'iocb' variable in iomap_dio_bio_end_io() Jens Axboe
2023-07-18 19:49 ` [PATCH 5/5] iomap: support IOCB_DIO_DEFER Jens Axboe
2023-07-18 23:50   ` Dave Chinner
2023-07-19 19:55     ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2023-07-11 20:33 [PATCHSET 0/5] Improve async iomap DIO performance Jens Axboe
2023-07-11 20:33 ` [PATCH 2/5] fs: add IOCB flags related to passing back dio completions Jens Axboe

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox