The patch 54efd50bfd873e2dbf784e0b21a8027ba4299a3e ("block: make
generic_make_request handle arbitrarily sized bios") makes it possible for
block devices to process large bios. The patch allocates a new bio set
queue->bio_split for each device, this bio set is used for allocating bios
when the driver needs to split large bios.
Each bio_set allocates a workqueue process, thus the above patch increases
the number of processes allocated per block device.
Device mapper doesn't need the queue->bio_split bio_set, thus we can
deallocate it. This reduces the number of allocated processes per
dm-device from 3 to 2.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm.c | 6 ++++++
1 file changed, 6 insertions(+)
Index: linux-4.3-rc4/drivers/md/dm.c
===================================================================
--- linux-4.3-rc4.orig/drivers/md/dm.c 2015-10-08 16:23:09.000000000 +0200
+++ linux-4.3-rc4/drivers/md/dm.c 2015-10-08 16:30:40.000000000 +0200
@@ -2839,6 +2839,12 @@ int dm_setup_md_queue(struct mapped_devi
case DM_TYPE_BIO_BASED:
dm_init_old_md_queue(md);
blk_queue_make_request(md->queue, dm_make_request);
+ /*
+ * We don't need the bioset, so we free it to save one process
+ * per device.
+ */
+ bioset_free(md->queue->bio_split);
+ md->queue->bio_split = NULL;
break;
}
--
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