On 17/08/24 05:23AM, Matthew Wilcox wrote:
On Thu, Jul 11, 2024 at 10:37:46AM +0530, Kundan Kumar wrote:-bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv, - struct page *page, unsigned len, unsigned offset, +bool bvec_try_merge_hw_folio(struct request_queue *q, struct bio_vec *bv, + struct folio *folio, size_t len, size_t offset, bool *same_page) { + struct page *page = folio_page(folio, 0); unsigned long mask = queue_segment_boundary(q); phys_addr_t addr1 = bvec_phys(bv); phys_addr_t addr2 = page_to_phys(page) + offset + len - 1;[...]+bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv, + struct page *page, unsigned int len, unsigned int offset, + bool *same_page) +{ + struct folio *folio = page_folio(page); + + return bvec_try_merge_hw_folio(q, bv, folio, len, + ((size_t)folio_page_idx(folio, page) << PAGE_SHIFT) + + offset, same_page); +}This is the wrong way to do it. bio_add_folio() does it correctly by being a wrapper around bio_add_page(). The reason is that in the future, not all pages will belong to folios. For those pages, page_folio() will return NULL, and this will crash.
I can change in this fashion. page_folio is getting used at many other places in kernel and currently there are no NULL checks. Will every place need a change? In this series we use page_folio to fetch folio for pages returned by iov_iter_extract_pages. Then we iterate on the folios instead of pages. We were progressing to change all the page related functions to accept struct folio. If page_folio may return NULL in future, it will require us to maintain both page and folio versions. Do you see it differently ?
