On 2022-05-27 13:03, Jason Gunthorpe wrote:
> On Fri, May 27, 2022 at 09:35:07AM -0600, Logan Gunthorpe wrote:
>>
>>
>> On 2022-05-27 06:55, Jason Gunthorpe wrote:
>>> On Thu, Apr 07, 2022 at 09:47:16AM -0600, Logan Gunthorpe wrote:
>>>> +static void pci_p2pdma_unmap_mappings(void *data)
>>>> +{
>>>> + struct pci_dev *pdev = data;
>>>> + struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
>>>> +
>>>> + /* Ensure no new pages can be allocated in mappings */
>>>> + p2pdma->active = false;
>>>> + synchronize_rcu();
>>>> +
>>>> + unmap_mapping_range(p2pdma->inode->i_mapping, 0, 0, 1);
>>>> +
>>>> + /*
>>>> + * On some architectures, TLB flushes are done with call_rcu()
>>>> + * so to ensure GUP fast is done with the pages, call synchronize_rcu()
>>>> + * before freeing them.
>>>> + */
>>>> + synchronize_rcu();
>>>> + pci_p2pdma_free_mappings(p2pdma->inode->i_mapping);
>>>
>>> With the series from Felix getting close this should get updated to
>>> not set pte_devmap and use proper natural refcounting without any of
>>> this stuff.
>>
>> Can you send a link? I'm not sure what you are referring to.
>
> IIRC this is the last part:
>
> https://lore.kernel.org/linux-mm/20220524190632.3304-1-alex.sierra@xxxxxxx/
>
> And the earlier bit with Christoph's pieces looks like it might get
> merged to v5.19..
>
> The general idea is once pte_devmap is not set then all the
> refcounting works the way it should. This is what all new ZONE_DEVICE
> users should do..
Ok, I don't actually follow how those patches relate to this.
Based on your description I guess I don't need to set PFN_DEV and
perhaps not use vmf_insert_mixed()? And then just use vm_normal_page()?
But the refcounting of the pages seemed like it was already sane to me,
unless you mean that the code no longer has to synchronize_rcu() before
returning the pages... that would be spectacular and clean things up a
lot (plus fix an annoying issue where if you use then free all the
memory you can't allocate new memory for an indeterminate amount of time).
Logan
