On Wed, Sep 25, 2024 at 4:51 PM David Matlack <dmatlack@xxxxxxxxxx> wrote: > > On 2024-09-13 02:43 PM, Vipin Sharma wrote: > > This series is extracted out from the NUMA aware page table series[1]. > > MMU shrinker changes were in patches 1 to 9 in the old series. > > I'm curious how you tested this series. Would it be posisble to write a > selftest to exercise KVM's shrinker interactions? I don't think it needs > to be anything fancy to be useful (e.g. just run a VM, trigger lots of > shrinking, and make sure nothing blows up). My testing was dropping caches (echo 2 > /proc/sys/vm/drop_caches) in background while running dirty_log_perf_test selftest multiple times. I added printk in shrink_count() and shrink_scan() to make sure pages are being reported and released. I can write a test which can spawn a thread to drop caches and a VM which touches all of its pages to generate page faults. Only downside is it will not detect if KVM MMU shrinker is being invoked, counting and freeing pages. > > There appears to be a debugfs interface which could be used to trigger > shrinking from a selftest. > > https://docs.kernel.org/admin-guide/mm/shrinker_debugfs.html This is interesting and it does what is needed to test KVM MMU shrinker. However, this needs CONFIG_DEBUG_FS and CONFIG_SHRINKER_DEBUG. I think using shrinker_debugfs will be better, selftest can just skip if it cannot find shrinker_debugfs files. One downside is that this test will not run if these configs are not enabled. Which one do you prefer? I am preferring shrinker_debugfs but concerned about its dependency on those two configs, not sure if it is okay to have this kind of dependency in a selftests.
