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block: provide plug based way of signaling forced no-wait semantics

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Provide a way for the caller to specify that IO should be marked
with REQ_NOWAIT to avoid blocking on allocation.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-06-04 11:23:39 -06:00
parent 2e0464d48f
commit 5a473e8311
2 changed files with 7 additions and 0 deletions
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6
block/blk-core.c
View file

@ -958,6 +958,7 @@ generic_make_request_checks(struct bio *bio)
struct request_queue *q;
int nr_sectors = bio_sectors(bio);
blk_status_t status = BLK_STS_IOERR;
struct blk_plug *plug;
char b[BDEVNAME_SIZE];
might_sleep();
@ -971,6 +972,10 @@ generic_make_request_checks(struct bio *bio)
goto end_io;
}
plug = blk_mq_plug(q, bio);
if (plug && plug->nowait)
bio->bi_opf |= REQ_NOWAIT;
/*
* For a REQ_NOWAIT based request, return -EOPNOTSUPP
* if queue is not a request based queue.
@ -1800,6 +1805,7 @@ void blk_start_plug(struct blk_plug *plug)
INIT_LIST_HEAD(&plug->cb_list);
plug->rq_count = 0;
plug->multiple_queues = false;
plug->nowait = false;
/*
* Store ordering should not be needed here, since a potential

1
include/linux/blkdev.h
View file

@ -1189,6 +1189,7 @@ struct blk_plug {
struct list_head cb_list; /* md requires an unplug callback */
unsigned short rq_count;
bool multiple_queues;
bool nowait;
};
#define BLK_MAX_REQUEST_COUNT 16
#define BLK_PLUG_FLUSH_SIZE (128 * 1024)