Hi, the block layer has a flag - QUEUE_FLAG_CLUSTER - which can be set (well, can be cleared, it defaults to set) by device drivers to encourage clustering of blocks in a bio - the presence of the flag essentially allows bios to be made bigger. Currently this flag is not set for dm (or md) devices, so bios are not made a big as they could be in some cases. The following patch sets the flag in the dm device, if all of the underlying devices have it set. NeilBrown ------------ This flag should be set for a virtual device iff it is set for all underlying devices. Signed-off-by: Neil Brown <neilb@xxxxxxx> ### Diffstat output ./drivers/md/dm-table.c | 9 +++++++++ ./include/linux/device-mapper.h | 1 + 2 files changed, 10 insertions(+) diff ./drivers/md/dm-table.c~current~ ./drivers/md/dm-table.c --- ./drivers/md/dm-table.c~current~ 2005-12-07 14:07:56.000000000 +1100 +++ ./drivers/md/dm-table.c 2005-12-07 14:14:46.000000000 +1100 @@ -97,6 +97,8 @@ static void combine_restrictions_low(str lhs->seg_boundary_mask = min_not_zero(lhs->seg_boundary_mask, rhs->seg_boundary_mask); + + lhs->no_cluster |= rhs->no_cluster; } /* @@ -525,6 +527,8 @@ int dm_get_device(struct dm_target *ti, rs->seg_boundary_mask = min_not_zero(rs->seg_boundary_mask, q->seg_boundary_mask); + + rs->no_cluster |= !test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); } return r; @@ -834,6 +838,11 @@ void dm_table_set_restrictions(struct dm q->hardsect_size = t->limits.hardsect_size; q->max_segment_size = t->limits.max_segment_size; q->seg_boundary_mask = t->limits.seg_boundary_mask; + if (t->limits.no_cluster) + q->queue_flags &= ~(1 << QUEUE_FLAG_CLUSTER); + else + q->queue_flags |= (1 << QUEUE_FLAG_CLUSTER); + } unsigned int dm_table_get_num_targets(struct dm_table *t) diff ./include/linux/device-mapper.h~current~ ./include/linux/device-mapper.h --- ./include/linux/device-mapper.h~current~ 2005-12-07 14:07:56.000000000 +1100 +++ ./include/linux/device-mapper.h 2005-12-07 14:14:46.000000000 +1100 @@ -97,6 +97,7 @@ struct io_restrictions { unsigned short hardsect_size; unsigned int max_segment_size; unsigned long seg_boundary_mask; + unsigned char no_cluster; /* inverted so that 0 is default */ }; struct dm_target { -- dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel