Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > > Replace BIO_NO_PAGE_REF with a BIO_PAGE_REFFED flag that has the inverted > > meaning is only set when a page reference has been acquired that needs to > > be released by bio_release_pages(). > > What was the motivation for this patch? We need to move to using FOLL_PIN for buffers derived from direct I/O to avoid the fork vs async-DIO race. Further, we shouldn't be taking a ref or a pin on pages derived from internal kernel iterators such as KVEC or BVEC as the page refcount might not be a valid way to control the lifetime of the data/buffers in those pages (slab, for instance). Rather, for internal kernel I/O, we need to rely on the caller to hold onto the memory until we tell them we've finished. So we flip the polarity of the page-is-ref'd flag and then add a page-is-pinned flag. The intention is to ultimately drop the page-is-ref'd flag - but we still need to keep the page-is-pinned flag. This makes it easier to take a stepwise approach - and having both flags working the same way makes the logic easier to follow. See iov_iter_extract_pages() and iov_iter_extract_will_pin(). David
