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. >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. I will try to go through the patch more carefully later as time allows. > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> -- Michal Hocko SUSE Labs
