On Thu, Sep 22, 2022 at 01:29:35PM +0200, Jan Kara wrote: > > This rule would mostly work, as long as we can relax it in some cases, to > > allow pinning of both source and dest pages, instead of just destination > > pages, in some cases. In particular, bio_release_pages() has lost all > > context about whether it was a read or a write request, as far as I can > > tell. And bio_release_pages() is the primary place to unpin pages for > > direct IO. > > Well, we already do have BIO_NO_PAGE_REF bio flag that gets checked in > bio_release_pages(). I think we can easily spare another bio flag to tell > whether we need to unpin or not. So as long as all the pages in the created > bio need the same treatment, the situation should be simple. Yes. Incidentally, the same condition is already checked by the creators of those bio - see the assorted should_dirty logics. While we are at it - how much of the rationale around bio_check_pages_dirty() doing dirtying is still applicable with pinning pages before we stick them into bio? We do dirty them before submitting bio, then on completion bio_check_pages_dirty() checks if something has marked them clean while we'd been doing IO; if all of them are still dirty we just drop the pages (well, unpin and drop), otherwise we arrange for dirty + unpin + drop done in process context (via schedule_work()). Can they be marked clean by anyone while they are pinned? After all, pinning is done to prevent writeback getting done on them while we are modifying the suckers...
