On Mon, Aug 24, 2026 at 09:02:30AM +0200, Maxime Ripard wrote: > On Fri, Aug 21, 2026 at 02:56:55PM -0400, Eric Chanudet wrote: > > Add a cgroup v2 mount option that will be used later in this series to > > enable CMA memory accounting under memcg. > > > > The option is made opt-in as it will charge allocations to the cgroup's > > overall memory usage, which changes existing expectations. > > > > Signed-off-by: Eric Chanudet <[email protected]> > > --- > > Documentation/admin-guide/cgroup-v2.rst | 20 ++++++++++++++++++++ > > include/linux/cgroup-defs.h | 5 +++++ > > kernel/cgroup/cgroup.c | 15 ++++++++++++++- > > 3 files changed, 39 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/admin-guide/cgroup-v2.rst > > b/Documentation/admin-guide/cgroup-v2.rst > > index aed195a71cbf..3dfc13f31a0c 100644 > > --- a/Documentation/admin-guide/cgroup-v2.rst > > +++ b/Documentation/admin-guide/cgroup-v2.rst > > @@ -246,6 +246,26 @@ cgroup v2 currently supports the following mount > > options. > > will not be tracked by the memory controller (even if cgroup > > v2 is remounted later on). > > > > + memory_cma_accounting > > + Count CMA memory usage towards the cgroup's overall memory usage > > for > > + the memory controller, and expose per-CMA-area usage counters. This > > + behavior is opt-in, so as to not cause regression on existing > > setups. > > + > > + A few caveats to keep in mind: > > + > > + * CMA areas are reserved at boot time, memory is only charged to a > > + cgroup when a CMA allocation is performed on its behalf. > > + * CMA pages allocated while this option is not enabled will not be > > + tracked by the memory controller, even if cgroup v2 is remounted > > + later on with this option. Charges happen at allocation. > > And what would happen if it's the other way around, ie mounted with this > option enabled, then remounted with the option disabled?
I meant for it to have no more charge issued until remounted with the option enabled. Pages that have been charged are uncharged when released, even if memory_cma_accounting is disabled after the charge is issued. In this version, it is broken[1]. I extended the documentation line with the fix for a potential v2. [1]https://lore.kernel.org/sashiko-reviews/[email protected]/ -- Eric Chanudet
