On Mon, Oct 23, 2017 at 7:49 PM, Michal Hocko <mhocko@xxxxxxxx> wrote: > 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. I see your point. But we are beginning to build on top of this. I'll just add it as a private patch in my patchset. But soon, we'll need to address HMM/CDM pages of different sizes as well. My problem right now is to ensure correctness of the design and expectations and a large part of it is tracking where the pages are. Balbir Singh. -- 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>
