On Tuesday February 6, [email protected] wrote:
> On Wed, 7 Feb 2007 10:26:56 +1100
> Neil Brown <[email protected]> wrote:
>
> > +static int bio_fits_rdev(struct bio *bi)
> > +{
> > + request_queue_t *q = bdev_get_queue(bi->bi_bdev);
> > +
> > + if ((bi->bi_size>>9) > q->max_sectors)
> > + return 0;
> > + blk_recount_segments(q, bi);
> > + if (bi->bi_phys_segments > q->max_phys_segments ||
> > + bi->bi_hw_segments > q->max_hw_segments)
> > + return 0;
> > +
> > + if (q->merge_bvec_fn)
> > + /* it's too hard to apply the merge_bvec_fn at this stage,
> > + * just just give up
> > + */
> > + return 0;
> > +
> > + return 1;
> > +}
>
> Isn't think going to return 0 rather a lot of the time?
Why do you say that?
merge_bvec_fn is only set for dm, md, pktcdvd.c so what won't cause a
zero in real-world cases (it rarely makes sense to put a raid5 on top
of those things).
So it will only return zero when ->max_sectors or ->max_*_segments are
less than the default, and while there are certainly quite a few of
those I wouldn't have expected them to be a majority (else we would
have had more complaints from -mm testers).
Yes, we should find the minimum of those values for devices currently
in the array and use that information in raid5's merge_bvec_fn to stop
bios growing too large. That would make it return 0 somewhat less
often.
But I think for a lot of modern hardware, it won't return 0 at all....
or am I just not seeing some really obvious typo that you can see ??
NeilBrown
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