On Sun, Oct 23 2005, Jeff Garzik wrote: > Douglas Gilbert wrote: > >Which in turn makes me think of applying the same idea > >to max_sectors > > > > shost->max_sectors = MAX_512B_SECTORS_UNLIMITED; > > > Won't work. max_sectors is communicated to the block layer, where we > limit the overall size of the request for practical reasons. > > Read the comment in libata-scsi's slave_configure: > > /* TODO: 1024 is an arbitrary number, not the > * hardware maximum. This should be increased to > * 65534 when Jens Axboe's patch for dynamically > * determining max_sectors is merged. > */ > > Right now, setting the true hardware / command set maximum would use way > too much memory, with no way to get feedback from the VM. > > This is why SCSI_DEFAULT_MAX_SECTORS is defined to 1024. The block layer has had split values for quite some time, ->max_sectors and max_hw_sectors. scsi_ioctl.c needs a patch to look at max_hw_sectors instead and SCSI drivers could then easily be updated to advertise a real hardware value as well. That is what shost->max_sectors should be, SCSI mid layer would then set q->max_sectors to SCSI_DEFAULT_MAX_SECTORS and q->max_hw_sectors to shost->max_sectors. Then the limiting factor becomes BIO_MAX_PAGES for mapping in the user data, which caps us at 1MiB currently. -- Jens Axboe - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
