On Tue, Jul 23, 2019 at 04:59:07PM +0300, Konstantin Khlebnikov wrote: > > > On 23.07.2019 16:46, Joel Fernandes wrote: > > On Tue, Jul 23, 2019 at 02:54:26PM +0300, Konstantin Khlebnikov wrote: > > > The page_idle tracking feature currently requires looking up the pagemap > > > for a process followed by interacting with /sys/kernel/mm/page_idle. > > > This is quite cumbersome and can be error-prone too. If between > > > accessing the per-PID pagemap and the global page_idle bitmap, if > > > something changes with the page then the information is not accurate. > > > More over 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 simplified interface which works only with mapped pages: > > > Run: "echo 6 > /proc/pid/clear_refs" to mark all mapped pages as idle. > > > Pages that still idle are marked with bit 57 in /proc/pid/pagemap. > > > Total size of idle pages is shown in /proc/pid/smaps (_rollup). > > > > > > Piece of comment is stolen from Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> > > > > This will not work well for the problem at hand, the heap profiler > > (heapprofd) only wants to clear the idle flag for the heap memory area which > > is what it is profiling. There is no reason to do it for all mapped pages. > > Using the /proc/pid/page_idle in my patch, it can be done selectively for > > particular memory areas. > > > > I had previously thought of having an interface that accepts an address > > range to set the idle flag, however that is also more complexity. > > Profiler could look into particular area in /proc/pid/smaps > or count idle pages via /proc/pid/pagemap. > > Selective /proc/pid/clear_refs is not so hard to add. > Somthing like echo "6 561214d03000-561214d29000" > /proc/pid/clear_refs > might be useful for all other operations. This seems really odd of an interface. Also I don't see how you can avoid looking up reverse maps to determine if a page is really idle. What is also more odd is that traditionally clear_refs does interfere with reclaim due to clearing of accessed bit. Now you have one of the interfaces with clear_refs that does not interfere with reclaim. That is makes it very inconsistent. Also in this patch you have 2 interfaces to solve this, where as my patch added a single clean interface that is easy to use and does not need parsing of address ranges. All in all, I don't see much the point of this honestly. But thanks for poking at it. thanks, - Joel
