On Sat, Aug 14, 2021 at 04:57:06PM +0800, Ming Lei wrote:
> > + if (bitmap)
> > + max_sectors = min_t(int, max_sectors, BIO_MAX_VECS * PAGE_SIZE);
>
> s/PAGE_SIZE/PAGE_SECTORS
Yeah, max_sectors is in size units, I messed that up.
>
> > +
> > if (max_sectors < bio_sectors(bio)) {
> > struct bio *split = bio_split(bio, max_sectors,
> > GFP_NOIO, &conf->bio_split);
> >
>
> Here the limit is max single-page vectors, and the above way may not work,
> such as:
>
> 0 ~ 254: each bvec's length is 512
> 255: bvec's length is 8192
>
> the total length is just 512*255 + 8192 = 138752 bytes = 271 sectors, but it
> still may need 257 bvecs, which can't be allocated via bio_alloc_bioset().
Yes, we still need the rounding magic that alloc_behind_master_bio uses
here.
> One solution is to add queue limit of max_single_page_bvec, and let
> blk_queue_split() handle it.
I'd rather not bloat the core with this.
