On 1/7/21 11:30 AM, Daniel Vetter wrote:
On Thu, Jan 07, 2021 at 11:26:52AM -0500, Andrey Grodzovsky wrote:
On 1/7/21 11:21 AM, Daniel Vetter wrote:
On Tue, Jan 05, 2021 at 04:04:16PM -0500, Andrey Grodzovsky wrote:
On 11/23/20 3:01 AM, Christian König wrote:
Am 23.11.20 um 05:54 schrieb Andrey Grodzovsky:
On 11/21/20 9:15 AM, Christian König wrote:
Am 21.11.20 um 06:21 schrieb Andrey Grodzovsky:
Will be used to reroute CPU mapped BO's page faults once
device is removed.
Uff, one page for each exported DMA-buf? That's not something we can do.
We need to find a different approach here.
Can't we call alloc_page() on each fault and link them together
so they are freed when the device is finally reaped?
For sure better to optimize and allocate on demand when we reach
this corner case, but why the linking ?
Shouldn't drm_prime_gem_destroy be good enough place to free ?
I want to avoid keeping the page in the GEM object.
What we can do is to allocate a page on demand for each fault and link
the together in the bdev instead.
And when the bdev is then finally destroyed after the last application
closed we can finally release all of them.
Christian.
Hey, started to implement this and then realized that by allocating a page
for each fault indiscriminately
we will be allocating a new page for each faulting virtual address within a
VA range belonging the same BO
and this is obviously too much and not the intention. Should I instead use
let's say a hashtable with the hash
key being faulting BO address to actually keep allocating and reusing same
dummy zero page per GEM BO
(or for that matter DRM file object address for non imported BOs) ?
Why do we need a hashtable? All the sw structures to track this should
still be around:
- if gem_bo->dma_buf is set the buffer is currently exported as a dma-buf,
so defensively allocate a per-bo page
- otherwise allocate a per-file page
That exactly what we have in current implementation
Or is the idea to save the struct page * pointer? That feels a bit like
over-optimizing stuff. Better to have a simple implementation first and
then tune it if (and only if) any part of it becomes a problem for normal
usage.
Exactly - the idea is to avoid adding extra pointer to drm_gem_object,
Christian suggested to instead keep a linked list of dummy pages to be
allocated on demand once we hit a vm_fault. I will then also prefault the entire
VA range from vma->vm_end - vma->vm_start to vma->vm_end and map them
to that single dummy page.
This strongly feels like premature optimization. If you're worried about
the overhead on amdgpu, pay down the debt by removing one of the redundant
pointers between gem and ttm bo structs (I think we still have some) :-)
Until we've nuked these easy&obvious ones we shouldn't play "avoid 1
pointer just because" games with hashtables.
-Daniel
Well, if you and Christian can agree on this approach and suggest maybe what
pointer is
redundant and can be removed from GEM struct so we can use the 'credit' to add
the dummy page
to GEM I will be happy to follow through.
P.S Hash table is off the table anyway and we are talking only about linked list
here since by prefaulting
the entire VA range for a vmf->vma i will be avoiding redundant page faults to
same VMA VA range and so
don't need to search and reuse an existing dummy page but simply create a new
one for each next fault.
Andrey
Andrey
-Daniel
Andrey
Andrey
Regards,
Christian.
Signed-off-by: Andrey Grodzovsky <andrey.grodzov...@amd.com>
---
drivers/gpu/drm/drm_file.c | 8 ++++++++
drivers/gpu/drm/drm_prime.c | 10 ++++++++++
include/drm/drm_file.h | 2 ++
include/drm/drm_gem.h | 2 ++
4 files changed, 22 insertions(+)
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 0ac4566..ff3d39f 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -193,6 +193,12 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
goto out_prime_destroy;
}
+ file->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!file->dummy_page) {
+ ret = -ENOMEM;
+ goto out_prime_destroy;
+ }
+
return file;
out_prime_destroy:
@@ -289,6 +295,8 @@ void drm_file_free(struct drm_file *file)
if (dev->driver->postclose)
dev->driver->postclose(dev, file);
+ __free_page(file->dummy_page);
+
drm_prime_destroy_file_private(&file->prime);
WARN_ON(!list_empty(&file->event_list));
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 1693aa7..987b45c 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -335,6 +335,13 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
ret = drm_prime_add_buf_handle(&file_priv->prime,
dma_buf, *handle);
+
+ if (!ret) {
+ obj->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!obj->dummy_page)
+ ret = -ENOMEM;
+ }
+
mutex_unlock(&file_priv->prime.lock);
if (ret)
goto fail;
@@ -1020,6 +1027,9 @@ void drm_prime_gem_destroy(struct
drm_gem_object *obj, struct sg_table *sg)
dma_buf_unmap_attachment(attach, sg, DMA_BIDIRECTIONAL);
dma_buf = attach->dmabuf;
dma_buf_detach(attach->dmabuf, attach);
+
+ __free_page(obj->dummy_page);
+
/* remove the reference */
dma_buf_put(dma_buf);
}
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 716990b..2a011fc 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -346,6 +346,8 @@ struct drm_file {
*/
struct drm_prime_file_private prime;
+ struct page *dummy_page;
+
/* private: */
#if IS_ENABLED(CONFIG_DRM_LEGACY)
unsigned long lock_count; /* DRI1 legacy lock count */
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 337a483..76a97a3 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -311,6 +311,8 @@ struct drm_gem_object {
*
*/
const struct drm_gem_object_funcs *funcs;
+
+ struct page *dummy_page;
};
/**
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