On Fri, 15 Apr 2022 17:27:51 -0700 Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > There are 50+ different shrinkers in the kernel, many with their own bells and > whistles. Under the memory pressure the kernel applies some pressure on each of > them in the order of which they were created/registered in the system. Some > of them can contain only few objects, some can be quite large. Some can be > effective at reclaiming memory, some not. > > The only existing debugging mechanism is a couple of tracepoints in > do_shrink_slab(): mm_shrink_slab_start and mm_shrink_slab_end. They aren't > covering everything though: shrinkers which report 0 objects will never show up, > there is no support for memcg-aware shrinkers. Shrinkers are identified by their > scan function, which is not always enough (e.g. hard to guess which super > block's shrinker it is having only "super_cache_scan"). They are a passive > mechanism: there is no way to call into counting and scanning of an individual > shrinker and profile it. > > To provide a better visibility and debug options for memory shrinkers > this patchset introduces a /sys/kernel/shrinker interface, to some extent > similar to /sys/kernel/slab. > > For each shrinker registered in the system a folder is created. Please, "directory". > The folder > contains "count" and "scan" files, which allow to trigger count_objects() > and scan_objects() callbacks. For memcg-aware and numa-aware shrinkers > count_memcg, scan_memcg, count_node, scan_node, count_memcg_node > and scan_memcg_node are additionally provided. They allow to get per-memcg > and/or per-node object count and shrink only a specific memcg/node. > > To make debugging more pleasant, the patchset also names all shrinkers, > so that sysfs entries can have more meaningful names. I also was wondering "why not debugfs". > Usage examples: > > ... > > If the output doesn't fit into a single page, "...\n" is printed at the end of > output. Unclear. At the end of what output? > > Roman Gushchin (5): > mm: introduce sysfs interface for debugging kernel shrinker > mm: memcontrol: introduce mem_cgroup_ino() and > mem_cgroup_get_from_ino() > mm: introduce memcg interfaces for shrinker sysfs > mm: introduce numa interfaces for shrinker sysfs > mm: provide shrinkers with names > > arch/x86/kvm/mmu/mmu.c | 2 +- > ... > Nothing under Documentation/!
