Re: [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path

On Mon, Jun 07, 2021 at 06:35:39PM +0800, Coly Li wrote:

• /* Limitation for valid replace key size and cache_bio bvecs number */
• size_limit = min_t(unsigned int, bio_max_segs(UINT_MAX) * PAGE_SECTORS,

• 	   (1 << KEY_SIZE_BITS) - 1);
  

bio_max_segs kaps the argument to BIO_MAX_VECS, so you might as well directly write BIO_MAX_VECS. Can you explain the PAGE_SECTORS here a bit more? Does this code path use discontiguous per-sector allocations? Preferably in a comment.

• s->insert_bio_sectors = min3(size_limit, sectors, bio_sectors(bio));

Also I don't really understand the units involved here. s->insert_bio_sectors, sectors, and bio_sectors is in unit of 512 byte sectors.

• miss = bio_next_split(bio, sectors, GFP_NOIO, &s->d->bio_split);

• miss = bio_next_split(bio, s->insert_bio_sectors, GFP_NOIO, &s->d->bio_split);

Overly long line.