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

From: Christoph Hellwig
Date: Mon Jun 07 2021 - 07:07:05 EST


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.