scatterlist: allow chaining to preallocated chunks

Blk-mq drivers usually preallocate their S/G list as part of the request,
but if we want to support the very large S/G lists currently supported by
the SCSI code that would tie up a lot of memory in the preallocated request
pool.  Add support to the scatterlist code so that it can initialize a
S/G list that uses a preallocated first chunks and dynamically allocated
additional chunks.  That way the scsi-mq code can preallocate a first
page worth of S/G entries as part of the request, and dynamically extend
the S/G list when needed.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Webb Scales <[email protected]>
Acked-by: Jens Axboe <[email protected]>
Tested-by: Bart Van Assche <[email protected]>
Tested-by: Robert Elliott <[email protected]>

0 files changed, 0 insertions, 0 deletions