On Wed, Dec 16, 2020 at 10:41:36AM -0800, Linus Torvalds wrote: > On Wed, Dec 16, 2020 at 9:07 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > > > If this looks fine, I'll submit a proper patch. > > That patch looks good to me. > > It would be good if somebody else looked it through - maybe I like it > just because I got to pee in the snow and make my mark. But i think > that filemap_map_pages() now looks a lot more understandable, and > having that pte_offset_map_lock() outside the loop should be good. It worth noting that after the change in the worth case scenario we will have additional ref/unref and lock/unlock of the page if we get deep enough into filemap_map_pmd(), but fail to map the page. Also if the range doesn't have a mappable page we would setup a page table into the PMD entry. It means we cannot have huge page mapped there later. It may be a bummer: getting the page table out of page table tree requires mmap_write_lock(). We also take ptl for cold page cache. It may increase ptl contention, but it should be negligible with split-ptl. -- Kirill A. Shutemov
