On Fri, Jun 26, 2026 at 03:04:48PM +0000, Brendan Jackman wrote: > On Fri Jun 26, 2026 at 2:38 PM UTC, Brendan Jackman wrote: > > On Tue Apr 21, 2026 at 2:43 PM UTC, Lorenzo Stoakes wrote: > >> On Fri, Apr 10, 2026 at 03:17:58PM +0000, Kalyazin, Nikita wrote: > >>> From: Nikita Kalyazin <[email protected]> > >>> > >>> Let's convert set_direct_map_*() to take an address instead of a page to > >>> prepare for adding helpers that operate on folios; it will be more > >>> efficient to convert from a folio directly to an address without going > >>> through a page first. > > > > Why is this more efficient? Isn't it a purely compile-time conversion? > > > > Indeed in the current implementation folio_address() is > > page_address(&folio->page) so it still goes through a page anyway, no? > > > > I might be missing context here about how this will look in the > > memdesc future. > > Sorry I failed to do the history search here, this was suggested by > Willy during the review here: > > https://lore.kernel.org/kvm/[email protected]/ > > Matthew Wilcox <[email protected]> wrote: > > The implementation isn't the greatest. None of the implementations > > of set_direct_map_valid_noflush() actually do anything with the struct > > page; they all call page_address() or page_to_virt() (fundamentally the > > same thing). > > But IMO the struct page isn't there to carry runtime information, it's a > type hint that this API operates on physical pages. Yes this is already > implied by the name but it also gives us a certain amount of safety > since it avoids unaligned or non-physmap addresses at compile time.
I think it's more historical thingy, the initial user was vmalloc::set_area_direct_map() that passed each page from vm->pages[] to set_direct_map functions. And yes, having a page there let's the implementation to go directly from the page to it's address in the direct map, even for highmem ... > > So converting folio->page->address is a bit inefficient. > > ... but yeah now I see this comes from Willy I definitely suspect I'm > missing memdesc insight here. > > > It feels like we should change set_direct_map_valid_noflush() to take a > > const void * and pass either page_address() or folio_address(), depending > > whether the caller has a page or a folio. What do you think? ... while with void * it's not necessarily one-to-one because void * can be a vmalloc address. -- Sincerely yours, Mike.
