Re: [PATCH v20 09/10] drm/shmem-helper: Switch drm_gem_shmem_vmap/vunmap to use pin/unpin

[Boris Brezillon]

On Fri, 4 Apr 2025 10:01:50 +0200
Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:

> >> In your case, vmap an pin both intent to hold the shmem pages in memory.
> >> They might be build on top of the same implementation, but one should
> >> not be implemented with the other because of their different meanings.  
> > But that's not what we do, is it? Sure, in drm_gem_shmem_vmap_locked(),
> > we call drm_gem_shmem_pin_locked(), but that's an internal function to
> > make sure the pages are allocated and stay around until
> > drm_gem_shmem_vunmap_locked() is called.
> >
> > I guess we could rename pin_count into hard_refcount or
> > page_residency_count or xxx_count, and change the pin/unpin_locked()
> > function names accordingly, but that's just a naming detail, it doesn't
> > force you to call drm_gem_pin() to vmap() your GEM, it's something we
> > do internally.  
> 
> Such a rename would be much appreciated. page_residency_count seems 
> appropriate.

On a second thought, I think I prefer
'unevictable_count/inc_unevictable()/dec_unevictable()'. But looking at
the gem-vram changes you just posted, it looks like gem-shmem is not the
only one to use the term 'pin' for this page pinning thing, so if we go
and plan for a rename, I'd rather make it DRM-wide than gem-shmem being
the outlier yet again :-).