[RFC,v3,5/8] dmabuf: Add gpu cgroup charge transfer function
Commit Message
From: Hridya Valsaraju <hridya@google.com>
The dma_buf_charge_transfer function provides a way for processes to
transfer charge of a buffer to a different process. This is essential
for the cases where a central allocator process does allocations for
various subsystems, hands over the fd to the client who requested the
memory and drops all references to the allocated memory.
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Signed-off-by: T.J. Mercier <tjmercier@google.com>
---
v3 changes
Use more common dual author commit message format per John Stultz.
v2 changes
Move dma-buf cgroup charge transfer from a dma_buf_op defined by every
heap to a single dma-buf function for all heaps per Daniel Vetter and
Christian König.
---
drivers/dma-buf/dma-buf.c | 48 +++++++++++++++++++++++++++++++++++++++
include/linux/dma-buf.h | 2 ++
2 files changed, 50 insertions(+)
Comments
Hello.
On Wed, Mar 09, 2022 at 04:52:15PM +0000, "T.J. Mercier" <tjmercier@google.com> wrote:
> +int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
> +{
> +#ifdef CONFIG_CGROUP_GPU
> + struct gpucg *current_gpucg;
> + int ret = 0;
> +
> + /*
> + * Verify that the cgroup of the process requesting the transfer is the
> + * same as the one the buffer is currently charged to.
> + */
> + current_gpucg = gpucg_get(current);
> + mutex_lock(&dmabuf->lock);
> + if (current_gpucg != dmabuf->gpucg) {
> + ret = -EPERM;
> + goto err;
> + }
Add a shortcut for gpucg == current_gpucg?
> +
> + ret = gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
> + if (ret)
> + goto err;
> +
> + dmabuf->gpucg = gpucg;
> +
> + /* uncharge the buffer from the cgroup it's currently charged to. */
> + gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);
I think gpucg_* API would need to cater for such transfers too since
possibly transitional breach of a limit during the transfer may
unnecessarily fail the operation.
My 0.02€,
Michal
On Mon, Mar 21, 2022 at 10:45 AM Michal Koutný <mkoutny@suse.com> wrote:
>
> Hello.
>
> On Wed, Mar 09, 2022 at 04:52:15PM +0000, "T.J. Mercier" <tjmercier@google.com> wrote:
> > +int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
> > +{
> > +#ifdef CONFIG_CGROUP_GPU
> > + struct gpucg *current_gpucg;
> > + int ret = 0;
> > +
> > + /*
> > + * Verify that the cgroup of the process requesting the transfer is the
> > + * same as the one the buffer is currently charged to.
> > + */
> > + current_gpucg = gpucg_get(current);
> > + mutex_lock(&dmabuf->lock);
> > + if (current_gpucg != dmabuf->gpucg) {
> > + ret = -EPERM;
> > + goto err;
> > + }
>
> Add a shortcut for gpucg == current_gpucg?
Good idea, thank you!
>
> > +
> > + ret = gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
> > + if (ret)
> > + goto err;
> > +
> > + dmabuf->gpucg = gpucg;
> > +
> > + /* uncharge the buffer from the cgroup it's currently charged to. */
> > + gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);
>
> I think gpucg_* API would need to cater for such transfers too since
> possibly transitional breach of a limit during the transfer may
> unnecessarily fail the operation.
Since the charge is duplicated in two cgroups for a short period
before it is uncharged from the source cgroup I guess the situation
you're thinking about is a global (or common ancestor) limit? I can
see how that would be a problem for transfers done this way and an
alternative would be to swap the order of the charge operations: first
uncharge, then try_charge. To be certain the uncharge is reversible if
the try_charge fails, I think I'd need either a mutex used at all
gpucg_*charge call sites or access to the gpucg_mutex, which implies
adding transfer support to gpu.c as part of the gpucg_* API itself and
calling it here. Am I following correctly here?
This series doesn't actually add limit support just accounting, but
I'd like to get it right here.
>
> My 0.02€,
> Michal
Thanks!
@@ -1374,6 +1374,54 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
}
EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
+/**
+ * dma_buf_charge_transfer - Change the GPU cgroup to which the provided dma_buf
+ * is charged.
+ * @dmabuf: [in] buffer whose charge will be migrated to a different GPU
+ * cgroup
+ * @gpucg: [in] the destination GPU cgroup for dmabuf's charge
+ *
+ * Only tasks that belong to the same cgroup the buffer is currently charged to
+ * may call this function, otherwise it will return -EPERM.
+ *
+ * Returns 0 on success, or a negative errno code otherwise.
+ */
+int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
+{
+#ifdef CONFIG_CGROUP_GPU
+ struct gpucg *current_gpucg;
+ int ret = 0;
+
+ /*
+ * Verify that the cgroup of the process requesting the transfer is the
+ * same as the one the buffer is currently charged to.
+ */
+ current_gpucg = gpucg_get(current);
+ mutex_lock(&dmabuf->lock);
+ if (current_gpucg != dmabuf->gpucg) {
+ ret = -EPERM;
+ goto err;
+ }
+
+ ret = gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
+ if (ret)
+ goto err;
+
+ dmabuf->gpucg = gpucg;
+
+ /* uncharge the buffer from the cgroup it's currently charged to. */
+ gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);
+
+err:
+ mutex_unlock(&dmabuf->lock);
+ gpucg_put(current_gpucg);
+ return ret;
+#else
+ return 0;
+#endif /* CONFIG_CGROUP_GPU */
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_charge_transfer, DMA_BUF);
+
#ifdef CONFIG_DEBUG_FS
static int dma_buf_debug_show(struct seq_file *s, void *unused)
{
@@ -646,4 +646,6 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
unsigned long);
int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
+
+int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg);
#endif /* __DMA_BUF_H__ */