Re: [PATCH v15 16/23] drm/shmem-helper: Use kref for vmap_use_count

[Dmitry Osipenko]

On 8/28/23 13:00, Boris Brezillon wrote:
> On Sun, 27 Aug 2023 20:54:42 +0300
> Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote:
> 
>> Use kref helper for vmap_use_count to make refcounting consistent with
>> pages_use_count and pages_pin_count that use kref. This will allow to
>> optimize unlocked vmappings by skipping reservation locking if refcnt > 1.
> 
> The core is taking the resv lock before calling ->v[un]map(), so
> switching to a kref sounds a bit premature/useless, unless there are
> plans to delegate the locking to the drivers. The only thing it brings
> is standard overflow/underflow checks. Not really sure it's worth
> transitioning to a kref for this field until we have a real use case.

The overflow checks worth transitioning. I'll mention them in the commit
message for v16.

-- 
Best regards,
Dmitry