On Mon, Jul 06, 2026 at 02:06:40PM +0200, Albert Esteve <[email protected]> wrote: > Currently, dmem charging is driver-driven through direct > calls to dmem_cgroup_try_charge(), so cgroup selftests > do not have a generic way to trigger charge and uncharge > paths from userspace. > > This limits any selftest coverage to configuration/readout > checks unless a specific driver exposing charge hooks is > present in the test environment.
What about that drivers/gpu/drm/ttm/tests/ttm_resource_test.c ? > > Add kernel/cgroup/dmem_selftest.c as a helper module > (CONFIG_DMEM_SELFTEST) that registers a synthetic dmem region > (dmem_selftest) and exposes debugfs control files: > /sys/kernel/debug/dmem_selftest/charge > /sys/kernel/debug/dmem_selftest/uncharge Nit: I'd think about alloc and free (to denote meaning not how it's implemented). > > Writing a size to charge triggers dmem_cgroup_try_charge() for > the calling task's cgroup (the module calls kstrtou64()). > Writing to uncharge releases the outstanding charge via > dmem_cgroup_uncharge(). Only a single outstanding charge > is supported. > > This provides a deterministic, driver-independent mechanism > for exercising dmem accounting paths in selftests. > > Signed-off-by: Albert Esteve <[email protected]> > --- > init/Kconfig | 12 +++ > kernel/cgroup/Makefile | 1 + > kernel/cgroup/dmem_selftest.c | 198 > ++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 211 insertions(+) > > diff --git a/init/Kconfig b/init/Kconfig > index 5230d4879b1c8..6fab65d6b44ea 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1267,6 +1267,18 @@ config CGROUP_DMEM > As an example, it allows you to restrict VRAM usage for applications > in the DRM subsystem. > > +config DMEM_SELFTEST > + tristate "dmem cgroup selftest helper module" > + depends on CGROUP_DMEM && DEBUG_FS > + default n > + help > + Builds a small loadable module that registers a dmem region named > + "dmem_selftest" and exposes debugfs files under > + /sys/kernel/debug/dmem_selftest/ so kselftests can trigger > + dmem charge/uncharge operations from userspace. > + > + Say N unless you run dmem selftests or develop the dmem controller. Could this be made w/out introduciton of a new Kconfig option? (E.g. what tools/testing/selftests/livepatch/test_modules/Makefile does) (Maybe reword to insmod if you choose building the test module as OOT.) > +static int __init dmem_selftest_register(void) Just an idea to reduce the amount debugfs of boilerplage -- the testing args could be handled by module_param_cb(). > +static int __init dmem_selftest_init(void) ... > + add_taint(TAINT_TEST, LOCKDEP_STILL_OK); Great!
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