Am 08.01.21 um 15:26 schrieb Andrey Grodzovsky:
Hey Christian, just a ping.
Was there any question for me here?
As far as I can see the best approach would still be to fill the VMA
with a single dummy page and avoid pointers in the GEM object.
Christian.
Andrey
On 1/7/21 11:37 AM, Andrey Grodzovsky wrote:
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
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