On Mon, Aug 22, 2022 at 09:34:59PM +0200, Michal Hocko wrote: > On Mon 22-08-22 11:37:30, Roman Gushchin wrote: > [...] > > I wonder only if we want to make it configurable (Idk a sysctl or maybe > > a config option) and close the topic. > > I do not think this is a good idea. We have other examples where we have > outsourced internal tunning to the userspace and it has mostly proven > impractical and long term more problematic than useful (e.g. > lowmem_reserve_ratio, percpu_pagelist_high_fraction, swappiness just to > name some that come to my mind). I have seen more often these to be used > incorrectly than useful. A agree, not a strong opinion here. But I wonder if somebody will complain on Shakeel's change because of the reduced accuracy. I know some users are using memory cgroups to track the size of various workloads (including relatively small) and 32->64 pages per cpu change can be noticeable for them. But we can wait for an actual bug report :) > > In this case, I guess we should consider either moving to per memcg > charge batching and see whether the pcp overhead x memcg_count is worth > that or some automagic tuning of the batch size depending on how > effectively the batch is used. Certainly a lot of room for > experimenting. I'm not a big believer into the automagic tuning here because it's a fundamental trade-off of accuracy vs performance and various users might make a different choice depending on their needs, not on the cpu count or something else. Per-memcg batching sounds interesting though. For example, we can likely batch updates on leaf cgroups and have a single atomic update instead of multiple most of the times. Or do you mean something different? Thanks!
