On Tue, Dec 08, 2020 at 05:51:32PM +0800, Muchun Song wrote: > The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), so the type of s32 > of lruvec_stat_cpu is enough. And introduce struct per_cpu_lruvec_stat > to optimize memory usage. > > The size of struct lruvec_stat is 304 bytes on 64 bits system. As it > is a per-cpu structure. So with this patch, we can save 304 / 2 * ncpu > bytes per-memcg per-node where ncpu is the number of the possible CPU. > If there are c memory cgroup (include dying cgroup) and n NUMA node in > the system. Finally, we can save (152 * ncpu * c * n) bytes. Honestly, I'm not convinced. Say, ncpu = 32, n = 2, c = 500. We're saving <5Mb of memory. If the machine has 128Gb of RAM, it's .000000003%. Using longs (s64) allows not to think too much about overflows and can also be slightly faster on 64-bit machines. Thanks!
