On Tue, May 20, 2025 at 3:00 AM Maxime Ripard <mrip...@kernel.org> wrote: > > We've discussed a number of times of how some heap names are bad, but > not really what makes a good heap name. > > Let's document what we expect the heap names to look like. > > Signed-off-by: Maxime Ripard <mrip...@kernel.org> > --- > Documentation/userspace-api/dma-buf-heaps.rst | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/Documentation/userspace-api/dma-buf-heaps.rst > b/Documentation/userspace-api/dma-buf-heaps.rst > index > 535f49047ce6450796bf4380c989e109355efc05..b24618e360a9a9ba0bd85135d8c1760776f1a37f > 100644 > --- a/Documentation/userspace-api/dma-buf-heaps.rst > +++ b/Documentation/userspace-api/dma-buf-heaps.rst > @@ -21,5 +21,24 @@ following heaps: > usually created either through the kernel commandline through the > `cma` parameter, a memory region Device-Tree node with the > `linux,cma-default` property set, or through the `CMA_SIZE_MBYTES` or > `CMA_SIZE_PERCENTAGE` Kconfig options. Depending on the platform, it > might be called ``reserved``, ``linux,cma``, or ``default-pool``. > + > +Naming Convention > +================= > + > +A good heap name is a name that: > + > +- Is stable, and won't change from one version to the other; > + > +- Describes the memory region the heap will allocate from, and will > + uniquely identify it in a given platform; > + > +- Doesn't use implementation details, such as the allocator; > + > +- Can describe intended usage. > +
Thanks again for sending this out. Sorry I've been spotty in some of the discussions (I'm really trying to step back from this area). I might only suggest you provide a bit more "why" to the list of qualities you highlight here, just to communicate more of the spirit/philosophy of how these might be judged or reviewed in the future. > +For example, assuming a platform with a reserved memory region located > +at the RAM address 0x42000000, intended to allocate video framebuffers, > +and backed by the CMA kernel allocator. Good names would be > +`memory@42000000` or `video@42000000`, but `cma-video` wouldn't. The point about avoiding the allocator details, just so I better understand the criteria: Would distinguishing from a contiguous pool vs non-contiguous in the name be considered ok? As it's a property of the buffer returned, and one that is critically important for some devices. Or do you intend that to be opaque, and the usage->heap mapping logic to provide that itself? (Effectively avoiding folks from being able to make potentially problematic assumptions from the name?) Similarly, how would you suggest naming a heap that provides 32bit allocations? Similarly for "protected' allocations, which are being proposed? thanks -john
