On Tue, Oct 29, 2019 at 03:06:21PM +0800, Ming Lei wrote:
> __blk_queue_split() may be a bit heavy for small BS(such as 512B, or
Maybe spell out block size. BS has another much less nice connotation.
> bch_bio_map() should be the only one which doesn't use bio_add_page(),
> so force to mark bio built via bch_bio_map() as MULTI_PAGE.
We really need to fix that up. I had patches back in the day which
Kent didn't particularly like for non-technical reason, that might serve
as a starting point.
> @@ -789,6 +794,10 @@ void __bio_add_page(struct bio *bio, struct page *page,
> bio->bi_iter.bi_size += len;
> bio->bi_vcnt++;
>
> + if (!bio_flagged(bio, BIO_MULTI_PAGE) && (bio->bi_vcnt >= 2 ||
> + (bio->bi_vcnt == 1 && len > PAGE_SIZE)))
> + bio_set_flag(bio, BIO_MULTI_PAGE);
This looks pretty ugly and does more (and more confusing) checks than
actually needed Maybe we need a little bio_is_multi_page helper to clean
this up a bit:
/*
* Check if the bio contains more than a page and thus needs special
* treatment in the bio splitting code.
*/
static inline bool bio_is_multi_page(struct bio *bio)
{
return bio->bi_vcnt > 1 || bio->bi_io_vec[0].bv_len > PAGE_SIZE;
}
and then this becomes:
if (!bio_flagged(bio, BIO_MULTI_PAGE) && bio_is_multi_page(bio))
Then again these checks are so cheap that we can just use the
bio_is_multi_page helper directly and skip the flag entirely.
