On Tue, Aug 20, 2024 at 1:28 PM Kundan Kumar <kundan.kumar@xxxxxxxxxxx> wrote:
>
> 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 ?
>
Gentle ping. Any feedback on this ?
