Re: [PATCH v6 6/6] drm/ttm: Use common ancestor of evictor and evictee as limit pool

[Michal Koutný <mkoutny@suse.com>]

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Hi.

On Fri, Mar 13, 2026 at 12:40:05PM +0100, Natalie Vock <natalie.vock@gmx.de> wrote:
> However, if we always calculate protection from the root cgroup, this
> breaks prioritization of sibling cgroups: If one cgroup was explicitly
> protected and its siblings were not, the protected cgroup should get
> higher priority, i.e. the protected cgroup should be able to steal from
> unprotected siblings. This only works if we restrict the protection
> calculation to the subtree shared by evictor and evictee.

When there are thee siblings A, B, C where A has protection and C is
doing a new allocation (evictor) but hits a limit on L, what effective
values to A would be applied in the respective cases below?

Case 1)

  L    dmem.max
  `- A dmem.low
  `- B
  `- C (alloc)

Case 2)

  L       dmem.max
  `- M    // dmem.low=0
     `- A dmem.low
     `- B
     `- C (alloc)

I think it should be the configured A:dmem.low in the first case but
zero in the latter case because M has no protection configured. -- Is
that correct?

Thanks,
Michal

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