From aaa53168cbcc486ca1927faac00bd99e81d4ff04 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 28 May 2024 13:32:34 +0200 Subject: dm: optimize flushes Device mapper sends flush bios to all the targets and the targets send it to the underlying device. That may be inefficient, for example if a table contains 10 linear targets pointing to the same physical device, then device mapper would send 10 flush bios to that device - despite the fact that only one bio would be sufficient. This commit optimizes the flush behavior. It introduces a per-target variable flush_bypasses_map - it is set when the target supports flush optimization - currently, the dm-linear and dm-stripe targets support it. When all the targets in a table have flush_bypasses_map, flush_bypasses_map on the table is set. __send_empty_flush tests if the table has flush_bypasses_map - and if it has, no flush bios are sent to the targets via the "map" method and the list dm_table->devices is iterated and the flush bios are sent to each member of the list. Signed-off-by: Mikulas Patocka Reviewed-by: Mike Snitzer Suggested-by: Yang Yang --- include/linux/device-mapper.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/linux') diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h index 82b2195efaca..3611b230d0aa 100644 --- a/include/linux/device-mapper.h +++ b/include/linux/device-mapper.h @@ -397,6 +397,21 @@ struct dm_target { * bio_set_dev(). NOTE: ideally a target should _not_ need this. */ bool needs_bio_set_dev:1; + + /* + * Set if the target supports flush optimization. If all the targets in + * a table have flush_bypasses_map set, the dm core will not send + * flushes to the targets via a ->map method. It will iterate over + * dm_table->devices and send flushes to the devices directly. This + * optimization reduces the number of flushes being sent when multiple + * targets in a table use the same underlying device. + * + * This optimization may be enabled on targets that just pass the + * flushes to the underlying devices without performing any other + * actions on the flush request. Currently, dm-linear and dm-stripe + * support it. + */ + bool flush_bypasses_map:1; }; void *dm_per_bio_data(struct bio *bio, size_t data_size); -- cgit