Re: readahead

[Jens Axboe <axboe@suse.de>]

On Tue, Apr 16 2002, Andrew Morton wrote:
> Andries.Brouwer@cwi.nl wrote:
> > 
> > ...
> >     Do these cards not have a request queue?
> > 
> > The kernel views them as SCSI disks.
> > So yes, I can do
> > 
> >    blockdev --setra 0 /dev/sdc
> > 
> > Unfortunately that does not help in the least.
> > Indeed, the only user of the readahead info is
> > readahead.c: get_max_readahead() and it does
> > 
> >         blk_ra_kbytes = blk_get_readahead(inode->i_dev) / 2;
> >         if (blk_ra_kbytes < VM_MIN_READAHEAD)
> >                 blk_ra_kbytes = VM_MAX_READAHEAD;
> > 
> > We need to distinguish between undefined, and explicily zero.
> 
> Yup.  The below (untested) patch should fix it up.  Assuming
> that all drivers use blk_init_queue(), and heaven knows if
> that's the case.  If not, the readahead window will have to be

set it in blk_queue_make_request(), please.

-- 
Jens Axboe