[PATCH 01/15] block: provide plug based way of signaling forced no-wait semantics

Jens Axboe
2020-06-18T14:46:28Z

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>
---
block/blk-core.c | 6 ++++++
include/linux/blkdev.h | 1 +
2 files changed, 7 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 03252af8c82c..62a4904db921 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -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
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8fd900998b4e..6e067dca94cf 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -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)
--
2.27.0