On Thu, Apr 21, 2022 at 06:58:48PM -0700, Roman Gushchin 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/debug/shrinker interface, to some extent > similar to /sys/kernel/slab. > > For each shrinker registered in the system a directory is created. The directory > 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 debugfs entries can have more meaningful names. > > v1: > 1) switched to debugfs, suggested by Mike, Andrew, Greg and others > 2) switched to seq_file API for output, no PAGE_SIZE limit anymore, by Andrew > 3) switched to down_read_killable(), suggested by Hillf > 4) dropped stateful filtering and "freed" returning, by Kent > 5) added docs, by Andrew Not quite true, gonna add it and also a cgroup tree inspection tool and send out v2. Thanks!
