On Thu, Mar 06, 2025 at 12:35:36AM +0100, Christoph Hellwig wrote: > On Thu, Mar 06, 2025 at 08:20:08AM +1100, Dave Chinner wrote: > > > + __bio_add_page(bio, virt_to_page(bp->b_addr), > > > + BBTOB(bp->b_length), > > > + offset_in_page(bp->b_addr)); > > > } > > > > How does offset_in_page() work with a high order folio? It can only > > return a value between 0 and (PAGE_SIZE - 1). > > Yes. > > > i.e. shouldn't this > > be: > > > > folio = kmem_to_folio(bp->b_addr); > > > > bio_add_folio_nofail(bio, folio, BBTOB(bp->b_length), > > offset_in_folio(folio, bp->b_addr)); > > > > That is also correct, but does a lot more work underneath as the > bio_vecs work in terms of pages. In the long run this should use > a bio_add_virt that hides all that (and the bio_vecs should move to > store physical addresses). For now the above is the simplest and > most efficient version. Can you add a comment that the code is done this way because of the mismatch between block layer API and mm object (folio/slab) handling APIs? Otherwise this code is going to look wrong every time I look at in future.... -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
