On Sat 21-10-17 08:55:59, Balbir Singh wrote: > On Sat, Oct 21, 2017 at 12:08 AM, Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Wed 18-10-17 17:31:23, Balbir Singh wrote: > >> With HMM, we can have either public or private zone > >> device pages. With private zone device pages, they should > >> show up as swapped entities. For public zone device pages > >> the smaps output can be confusing and incomplete. > >> > >> This patch adds a new attribute to just smaps to show > >> device memory usage. > > > > As this will become user API which we will have to maintain for ever I > > would really like to hear about who is going to use this information and > > what for. > > This is something I observed when running some tests with HMM/CDM. > The issue I had was that there was no visibility of what happened to the > pages after the following sequence > > 1. malloc/mmap pages > 2. migrate_vma() to ZONE_DEVICE (hmm/cdm space) > 3. look at smaps > > If we look at smaps after 1 and the pages are faulted in we can see the > pages for the region, but at point 3, there is absolutely no visibility of > what happened to the pages. I thought smaps is a good way to provide > the visibility as most developers use that interface. It's more to fix the > inconsistency I saw w.r.t visibility and accounting. Yes I can see how this can be confusing. But, well, I have grown overly cautious regarding user APIs over time. So I would rather not add something new until we have a real user with a usecase in mind. We can always add this later but once we have exposed the accounting we are bound to maintain it for ever. -- Michal Hocko SUSE Labs -- 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>
