Re: [PATCH v2.1 1/1] kernel/cgroup: Add "dmem" memory accounting cgroup

[Maxime Ripard <mripard@kernel.org>]

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Hi Geert,

On Tue, Jan 14, 2025 at 11:16:43AM +0100, Geert Uytterhoeven wrote:
> Hi Maarten,
> 
> On Wed, Dec 4, 2024 at 3:32 PM Maarten Lankhorst <dev@lankhorst.se> wrote:
> > This code is based on the RDMA and misc cgroup initially, but now
> > uses page_counter. It uses the same min/low/max semantics as the memory
> > cgroup as a result.
> >
> > There's a small mismatch as TTM uses u64, and page_counter long pages.
> > In practice it's not a problem. 32-bits systems don't really come with
> > >=4GB cards and as long as we're consistently wrong with units, it's
> > fine. The device page size may not be in the same units as kernel page
> > size, and each region might also have a different page size (VRAM vs GART
> > for example).
> >
> > The interface is simple:
> > - Call dmem_cgroup_register_region()
> > - Use dmem_cgroup_try_charge to check if you can allocate a chunk of memory,
> >   use dmem_cgroup__uncharge when freeing it. This may return an error code,
> >   or -EAGAIN when the cgroup limit is reached. In that case a reference
> >   to the limiting pool is returned.
> > - The limiting cs can be used as compare function for
> >   dmem_cgroup_state_evict_valuable.
> > - After having evicted enough, drop reference to limiting cs with
> >   dmem_cgroup_pool_state_put.
> >
> > This API allows you to limit device resources with cgroups.
> > You can see the supported cards in /sys/fs/cgroup/dmem.capacity
> > You need to echo +dmem to cgroup.subtree_control, and then you can
> > partition device memory.
> >
> > Co-developed-by: Friedrich Vock <friedrich.vock@gmx.de>
> > Signed-off-by: Friedrich Vock <friedrich.vock@gmx.de>
> > Co-developed-by: Maxime Ripard <mripard@kernel.org>
> > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
> 
> Thanks for your patch, which is now commit b168ed458ddecc17
> ("kernel/cgroup: Add "dmem" memory accounting cgroup") in drm/drm-next.
> 
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1128,6 +1128,7 @@ config CGROUP_PIDS
> >
> >  config CGROUP_RDMA
> >         bool "RDMA controller"
> > +       select PAGE_COUNTER
> 
> This change looks unrelated?
> 
> Oh, reading your response to the build error, this should have been below?

Indeed, good catch.

> >         help
> >           Provides enforcement of RDMA resources defined by IB stack.
> >           It is fairly easy for consumers to exhaust RDMA resources, which
> > @@ -1136,6 +1137,15 @@ config CGROUP_RDMA
> >           Attaching processes with active RDMA resources to the cgroup
> >           hierarchy is allowed even if can cross the hierarchy's limit.
> >
> > +config CGROUP_DMEM
> > +       bool "Device memory controller (DMEM)"
> > +       help
> > +         The DMEM controller allows compatible devices to restrict device
> > +         memory usage based on the cgroup hierarchy.
> > +
> > +         As an example, it allows you to restrict VRAM usage for applications
> > +         in the DRM subsystem.
> > +
> 
> Do you envision other users than DRM?
> Perhaps this should depend on DRM for now?

dma-buf heaps and v4l2 support are in progress right now.

Maxime

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