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block: Introduce elevator features

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Introduce the definition of elevator features through the
elevator_features flags in the elevator_type structure. Each flag can
represent a feature supported by an elevator. The first feature defined
by this patch is support for zoned block device sequential write
constraint with the flag ELEVATOR_F_ZBD_SEQ_WRITE, which is implemented
by the mq-deadline elevator using zone write locking.

Other possible features are IO priorities, write hints, latency targets
or single-LUN dual-actuator disks (for which the elevator could maintain
one LBA ordered list per actuator).

The required_elevator_features field is also added to the request_queue
structure to allow a device driver to specify elevator feature flags
that an elevator must support for the correct operation of the device
(e.g. device drivers for zoned block devices can have the
ELEVATOR_F_ZBD_SEQ_WRITE flag as a required feature).
The helper function blk_queue_required_elevator_features() is
defined for setting this new field.

With these two new fields in place, the elevator functions
elevator_match() and elevator_find() are modified to allow a user to set
only an elevator with a set of features that satisfies the device
required features. Elevators not matching the device requirements are
not shown in the device sysfs queue/scheduler file to prevent their use.

The "none" elevator can always be selected as before.

Reviewed-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Signed-off-by: Damien Le Moal <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Damien Le Moal 2019-09-05 18:51:31 +09:00 • committed by Jens Axboe
commit 68c43f133a
5 changed files with 67 additions and 11 deletions
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16
block/blk-settings.c
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@ -832,6 +832,22 @@ void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
}
EXPORT_SYMBOL_GPL(blk_queue_write_cache);
/**
* blk_queue_required_elevator_features - Set a queue required elevator features
* @q: the request queue for the target device
* @features: Required elevator features OR'ed together
*
* Tell the block layer that for the device controlled through @q, only the
* only elevators that can be used are those that implement at least the set of
* features specified by @features.
*/
void blk_queue_required_elevator_features(struct request_queue *q,
unsigned int features)
{
q->required_elevator_features = features;
}
EXPORT_SYMBOL_GPL(blk_queue_required_elevator_features);
static int __init blk_settings_init(void)
{
blk_max_low_pfn = max_low_pfn - 1;