On Wed 02-10-19 19:08:16, Daniel Colascione wrote: > On Wed, Oct 2, 2019 at 6:56 PM Qian Cai <cai@xxxxxx> wrote: > > > On Oct 2, 2019, at 4:29 PM, Daniel Colascione <dancol@xxxxxxxxxx> wrote: > > > > > > Adding the correct linux-mm address. > > > > > > > > >> +config SPLIT_RSS_COUNTING > > >> + bool "Per-thread mm counter caching" > > >> + depends on MMU > > >> + default y if NR_CPUS >= SPLIT_PTLOCK_CPUS > > >> + help > > >> + Cache mm counter updates in thread structures and > > >> + flush them to visible per-process statistics in batches. > > >> + Say Y here to slightly reduce cache contention in processes > > >> + with many threads at the expense of decreasing the accuracy > > >> + of memory statistics in /proc. > > >> + > > >> endmenu > > > > All those vague words are going to make developers almost impossible to decide the right selection here. It sounds like we should kill SPLIT_RSS_COUNTING at all to simplify the code as the benefit is so small vs the side-effect? > > Killing SPLIT_RSS_COUNTING would be my first choice; IME, on mobile > and a basic desktop, it doesn't make a difference. I figured making it > a knob would help allay concerns about the performance impact in more > extreme configurations. I do agree with Qian. Either it is really helpful (is it? probably on the number of cpus) and it should be auto-enabled or it should be dropped altogether. You cannot really expect people know how to enable this without a deep understanding of the MM internals. Not to mention all those users using distro kernels/configs. A config option sounds like a bad way forward. -- Michal Hocko SUSE Labs
