On Sat, Sep 18, 2021 at 11:04:40AM +1000, Dave Chinner wrote: > As for long term, everything in the page cache API needs to > transition to byte offsets and byte counts instead of units of > PAGE_SIZE and page->index. That's a more complex transition, but > AFAIA that's part of the future work Willy is intended to do with > folios and the folio API. Once we get away from accounting and > tracking everything as units of struct page, all the public facing > APIs that use those units can go away. Probably 95% of the places we use page->index and page->mapping aren't necessary because we've already got that information from the context we're in and removing them would be a useful cleanup - if we've already got that from context (e.g. we're looking up the page in the page cache, via i_pageS) eliminating the page->index or page->mapping use means we're getting rid of a data dependency so it's good for performance - but more importantly, those (much fewer) places in the code where we actually _do_ need page->index and page->mapping are really important places to be able to find because they're interesting boundaries between different components in the VM.
