tree 7e268b3e7359720ddd1e08adcd159df922661479
parent 512c781fd28cb401ee9f2843e32bf4640732c671
author Gioh Kim <gi-oh.kim@cloud.ionos.com> 1607595505 +0100
committer Jens Axboe <axboe@kernel.dk> 1608155763 -0700

block/rnbd-clt: Dynamically allocate sglist for rnbd_iu

The BMAX_SEGMENT static array for scatterlist is embedded in
rnbd_iu structure to avoid memory allocation in hot IO path.
In many cases, we do need only several sg entries because many IOs
have only several segments.

This patch change rnbd_iu to check the number of segments in the request
and allocate sglist dynamically.

For io path, use sg_alloc_table_chained to allocate sg list faster.

First it makes two sg entries after pdu of request.
The sg_alloc_table_chained uses the pre-allocated sg entries
if the number of segments of the request is less than two.
So it reduces the number of memory allocation.

Signed-off-by: Gioh Kim <gi-oh.kim@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>