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fs: add IOCB flags related to passing back dio completions

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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: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
2023-07-08 09:55:27 -06:00
parent 7b3c14d1a9
commit 9cf3516c29
1 changed files with 33 additions and 2 deletions
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35
include/linux/fs.h
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@@ -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
* 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)