On Tue, Aug 06, 2019 at 10:56:05AM +0200, Michal Hocko wrote: > On Mon 05-08-19 13:04:47, Joel Fernandes (Google) wrote: > > The page_idle tracking feature currently requires looking up the pagemap > > for a process followed by interacting with /sys/kernel/mm/page_idle. > > Looking up PFN from pagemap in Android devices is not supported by > > unprivileged process and requires SYS_ADMIN and gives 0 for the PFN. > > > > This patch adds support to directly interact with page_idle tracking at > > the PID level by introducing a /proc/<pid>/page_idle file. It follows > > the exact same semantics as the global /sys/kernel/mm/page_idle, but now > > looking up PFN through pagemap is not needed since the interface uses > > virtual frame numbers, and at the same time also does not require > > SYS_ADMIN. > > > > In Android, we are using this for the heap profiler (heapprofd) which > > profiles and pin points code paths which allocates and leaves memory > > idle for long periods of time. This method solves the security issue > > with userspace learning the PFN, and while at it is also shown to yield > > better results than the pagemap lookup, the theory being that the window > > where the address space can change is reduced by eliminating the > > intermediate pagemap look up stage. In virtual address indexing, the > > process's mmap_sem is held for the duration of the access. > > As already mentioned in one of the previous versions. The interface > seems sane and the usecase as well. So I do not really have high level > objections. That is great to know. > From a quick look at the patch I would just object to pulling swap idle > tracking into this patch because it makes the review harder and it is > essentially a dead code until a later patch. I am also not sure whether > that is really necessary and it really begs for an explicit > justification. Ok I will split it out, and also expand on the need for it a bit more. > > I will try to go through the patch more carefully later as time allows. Thanks a lot. > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > -- > Michal Hocko > SUSE Labs - Joel
