This is updated patch to reduce the number of processes. When we free
q->bio_split bioset, we must also avoid the call to blk_queue_split that
uses it. The call to blk_queue_split is useless because device mapper does
its own splitting.
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
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. We remove the call to blk_queue_split, it is not
needed because device mapper does its own splitting.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
Index: linux-4.3-rc6/drivers/md/dm.c
===================================================================
--- linux-4.3-rc6.orig/drivers/md/dm.c 2015-10-21 19:29:04.000000000 +0200
+++ linux-4.3-rc6/drivers/md/dm.c 2015-10-21 19:29:58.000000000 +0200
@@ -1742,8 +1742,6 @@ static void dm_make_request(struct reque
map = dm_get_live_table(md, &srcu_idx);
- blk_queue_split(q, &bio, q->bio_split);
-
generic_start_io_acct(rw, bio_sectors(bio), &dm_disk(md)->part0);
/* if we're suspended, we have to queue this io for later */
@@ -2770,6 +2768,12 @@ 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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