On 06/03/2014 01:01 PM, Naoya Horiguchi wrote: > On Tue, Jun 03, 2014 at 08:55:04AM -0700, Dave Hansen wrote: >> On 06/02/2014 11:18 PM, Naoya Horiguchi wrote: >>> And for patch 8, 9, and 10, I don't think it's good idea to add a new callback >>> which can handle both pmd and pte (because they are essentially differnt thing). >>> But the underneath idea of doing pmd_trans_huge_lock() in the common code in >>> walk_single_entry_locked() looks nice to me. So it would be great if we can do >>> the same thing in walk_pmd_range() (of linux-mm) to reduce code in callbacks. >> >> You think they are different, I think they're the same. :) >> >> What the walkers *really* care about is getting a leaf node in the page >> tables. They generally don't *care* whether it is a pmd or pte, they >> just want to know what its value is and how large it is. > > OK, I see your idea, so I think that we could go to the direction to > unify all p(gd|ud|md|te)_entry() callbacks. > And if we find the leaf entry in whatever level, we call the common entry > handler on the entry, right? That's a level farther than I took it, but I think it makes sense. Nobody is using the walkers for the purposes of looking at anything but leaf nodes. > It would takes some time and effort to make all users to fit to this new > scheme, so my suggestion is: > 1. move pmd locking to walk_pmd_range() (then, your locked_single_entry() > callback is equal to pmd_entry()) Yes, except that still means that each walker needs separate code for regular _and_ transparent huge pages. It would be nice to be able to have a single handler which handles both. > 2. let each existing user have its common entry handler, and connect it to > its pmd_entry() and/or pte_entry() to keep compatibility > 3. apply page table walker to potential users. > I'd like to keep pmd/pte_entry() until we complete phase 2., > because we could find something which let us change core code, > 4. and finaly replace all p(gd|ud|md|te)_entry() with a unified callback. > > Could you let me have a few days to work on 1.? > I think that it means your patch 8 is effectively merged on top of mine. > So your current problem will be solved. That sounds quite nice. >> I'd argue that they don't really ever need to actually know at which >> level they are in the page tables, just if they are at the bottom or >> not. Note that *NOBODY* sets a pud or pgd entry. That's because the >> walkers are 100% concerned about leaf nodes (pte's) at this point. > > Yes. BTW do you think we should pud_entry() and pgd_entry() immediately? > We can do it and it reduces some trivial evaluations, so it's optimized > a little. Yeah, we might as well. They're just wasted space at the moment. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>