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J . Mercier" , Kenny.Ho@amd.com, Christian =?iso-8859-1?Q?K=F6nig?= , Brian Welty , Tvrtko Ursulin Subject: Re: [PATCH 08/17] drm/cgroup: Track DRM clients per cgroup Message-ID: References: <20230712114605.519432-1-tvrtko.ursulin@linux.intel.com> <20230712114605.519432-9-tvrtko.ursulin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230712114605.519432-9-tvrtko.ursulin@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Wed, Jul 12, 2023 at 12:45:56PM +0100, Tvrtko Ursulin wrote: > +void drmcgroup_client_migrate(struct drm_file *file_priv) > +{ > + struct drm_cgroup_state *src, *dst; > + struct cgroup_subsys_state *old; > + > + mutex_lock(&drmcg_mutex); > + > + old = file_priv->__css; > + src = css_to_drmcs(old); > + dst = css_to_drmcs(task_get_css(current, drm_cgrp_id)); > + > + if (src != dst) { > + file_priv->__css = &dst->css; /* Keeps the reference. */ > + list_move_tail(&file_priv->clink, &dst->clients); > + } > + > + mutex_unlock(&drmcg_mutex); > + > + css_put(old); > +} > +EXPORT_SYMBOL_GPL(drmcgroup_client_migrate); So, you're implicitly migrating the fd to the latest ioctl user on the first access. While this may work for state-less control like usage time. This likely will cause problem if you later want to add stateful control for memory consumption. e.g. What happens if the new destination doesn't have enough budget to accommodate the fd's usage? Let's say we allow over-commit with follow-up reclaim or oom kill actions, if so, can we guarantee that all memory ownership for can always be updated? If not, what happens after failure? If DRM needs to transfer fd ownership with resources attached to it, it likely would be a good idea to make that an explicit operation so that the attempt can be verified and failed if necessary. Thanks. -- tejun