Provided by:
linux-doc-2.6.15_2.6.15-23.39_all 
NAME
blk_queue_bounce_limit - set bounce buffer limit for queue
SYNOPSIS
void blk_queue_bounce_limit (request_queue_t * q, u64 dma_addr);
ARGUMENTS
q the request queue for the device
dma_addr
bus address limit
DESCRIPTION
Different hardware can have different requirements as to what pages it
can do I/O directly to. A low level driver can call
blk_queue_bounce_limit to have lower memory pages allocated as bounce
buffers for doing I/O to pages residing above page. By default the
block layer sets this to the highest numbered ‘‘low’’ memory page.