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SubjectRe: readahead
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

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