Messages in this thread | | | Date | Tue, 11 Jun 2013 17:42:31 +0800 | From | Tang Chen <> | Subject | Re: [WiP]: aio support for migrating pages (Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version of get_user_pages() called get_user_pages_non_movable()) |
| |
Hi Benjamin,
Are you still working on this problem ?
Thanks. :)
On 05/21/2013 10:27 AM, Benjamin LaHaise wrote: > On Tue, May 21, 2013 at 10:07:52AM +0800, Tang Chen wrote: > .... >> I'm not saying using two callbacks before and after migration is better. >> I don't want to use address_space_operations is because there is no such >> member >> for anonymous pages. > > That depends on the nature of the pinning. For the general case of > get_user_pages(), you're correct that it won't work for anonymous memory. > >> In your idea, using a file mapping will create a >> address_space_operations. But >> I really don't think we can modify the way of memory allocation for all the >> subsystems who has this problem. Maybe not just aio and cma. That means if >> you want to pin pages in memory, you have to use a file mapping. This makes >> the memory allocation more complicated. And the idea should be known by all >> the subsystem developers. Is that going to happen ? > > Different subsystems will need to use different approaches to fixing the > issue. I doubt any single approach will work for everything. > >> I also thought about reuse one field of struct page. But as you said, there >> may not be many users of this functionality. Reusing a field of struct page >> will make things more complicated and lead to high coupling. > > What happens when more than one subsystem tries to pin a particular page? > What if it's a shared page rather than an anonymous page? > >> So, how about the other idea that Mel mentioned ? >> >> We create a 1-1 mapping of pinned page ranges and the pinner (subsystem >> callbacks and data), maybe a global list or a hash table. And then, we can >> find the callbacks. > > Maybe that is the simplest approach, but it's going to make get_user_pages() > slower and more complicated (as if it wasn't already). Maybe with all the > bells and whistles of per-cpu data structures and such you can make it work, > but I'm pretty sure someone running the large unmentionable benchmark will > complain about the performance regressions you're going to introduce. At > least in the case of the AIO ring buffer, using the address_space approach > doesn't introduce any new performance issues. There's also the bigger > question of if you can or cannot exclude get_user_pages_fast() from this. > In short: you've got a lot more work on your hands to do. > >> Thanks. :) > > Cheers, > > -ben
| |