Andrew Morton wrote: > On Tue, 22 Sep 2015 15:16:32 -0700 Greg Thelen <gthelen@xxxxxxxxxx> wrote: > >> mem_cgroup_read_stat() returns a page count by summing per cpu page >> counters. The summing is racy wrt. updates, so a transient negative sum >> is possible. Callers don't want negative values: >> - mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback. >> - oom reports and memory.stat shouldn't show confusing negative usage. >> - tree_usage() already avoids negatives. >> >> Avoid returning negative page counts from mem_cgroup_read_stat() and >> convert it to unsigned. > > Someone please remind me why this code doesn't use the existing > percpu_counter library which solved this problem years ago. > >> for_each_possible_cpu(cpu) > > and which doesn't iterate across offlined CPUs. I found [1] and [2] discussing memory layout differences between: a) existing memcg hand rolled per cpu arrays of counters vs b) array of generic percpu_counter The current approach was claimed to have lower memory overhead and better cache behavior. I assume it's pretty straightforward to create generic percpu_counter_array routines which memcg could use. Possibly something like this could be made general enough could be created to satisfy vmstat, but less clear. [1] http://www.spinics.net/lists/cgroups/msg06216.html [2] https://lkml.org/lkml/2014/9/11/1057 -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
