On Wed, Dec 09, 2020 at 10:31:55AM +0800, Muchun Song wrote: > On Wed, Dec 9, 2020 at 10:21 AM Roman Gushchin <guro@xxxxxx> wrote: > > > > 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. Actually the threshold can be as big as MEMCG_CHARGE_BATCH * PAGE_SIZE. It still fits into s32, but without explicitly saying it it's hard to understand why not choosing s8, as in vmstat.c. > > > > > > 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%. > > Hi Roman, > > When the cpu hotplug is enabled, the ncpu can be 256 on > some configurations. Also, the c can be more large when > there are many dying cgroup in the system. > > So the savings depends on the environment and > configurations. Right? Of course, but machines with more CPUs tend to have more RAM as well. Thanks!
