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authorTejun Heo <tj@kernel.org>2011-01-25 12:43:54 +0100
committerJens Axboe <jaxboe@fusionio.com>2011-01-25 12:43:54 +0100
commitae1b1539622fb46e51b4d13b3f9e5f4c713f86ae (patch)
treec5cb540141003a3ec7ebf0b8c6e01653ab6aaef5 /include/linux/elevator.h
parent143a87f4c9c629067afea5b6703d66ea88c82f8e (diff)
block: reimplement FLUSH/FUA to support merge
The current FLUSH/FUA support has evolved from the implementation which had to perform queue draining. As such, sequencing is done queue-wide one flush request after another. However, with the draining requirement gone, there's no reason to keep the queue-wide sequential approach. This patch reimplements FLUSH/FUA support such that each FLUSH/FUA request is sequenced individually. The actual FLUSH execution is double buffered and whenever a request wants to execute one for either PRE or POSTFLUSH, it queues on the pending queue. Once certain conditions are met, a flush request is issued and on its completion all pending requests proceed to the next sequence. This allows arbitrary merging of different type of flushes. How they are merged can be primarily controlled and tuned by adjusting the above said 'conditions' used to determine when to issue the next flush. This is inspired by Darrick's patches to merge multiple zero-data flushes which helps workloads with highly concurrent fsync requests. * As flush requests are never put on the IO scheduler, request fields used for flush share space with rq->rb_node. rq->completion_data is moved out of the union. This increases the request size by one pointer. As rq->elevator_private* are used only by the iosched too, it is possible to reduce the request size further. However, to do that, we need to modify request allocation path such that iosched data is not allocated for flush requests. * FLUSH/FUA processing happens on insertion now instead of dispatch. - Comments updated as per Vivek and Mike. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: "Darrick J. Wong" <djwong@us.ibm.com> Cc: Shaohua Li <shli@kernel.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'include/linux/elevator.h')
-rw-r--r--include/linux/elevator.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 4fd978e7eb83..86120c916fcc 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -167,6 +167,7 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
#define ELEVATOR_INSERT_BACK 2
#define ELEVATOR_INSERT_SORT 3
#define ELEVATOR_INSERT_REQUEUE 4
+#define ELEVATOR_INSERT_FLUSH 5
/*
* return values from elevator_may_queue_fn