it states the following.
Unfortunately that setup time is large enough in some versions of the lk 2.4 series to adversely impact direct IO performance. Also memory malloc()-ed in the user space tends to be made up of discontinuous pages seen from the SCSI adapter. This requires the sg driver to build heavily splintered scatter gather lists which is less than desirable. This limits the maximum transfer size to [(max_scsi_adapter_scatter_gather_elements - 1) * PAGE_SIZE]. [This is a _different_ scatter gather mechanism to that which the user sees in the sg interface based on iovec.]
I have grepped through /usr/src/linux-2.4/ with grep -R 'max_scsi_adapter' *
but, I can't find the variable. Does anyone know where to find it?