Re: [RFC simple allocator v1 0/2] Simple allocator

From: Laura Abbott
Date: Wed Jan 25 2017 - 04:13:19 EST

On 01/23/2017 09:35 AM, Daniel Vetter wrote:
On Fri, Jan 20, 2017 at 04:32:29PM +0100, Benjamin Gaignard wrote:
The goal of this RFC is to understand if a common ioctl for specific memory
regions allocations is needed/welcome.

Obviously it will not replace allocation done in linux kernel frameworks like
v4l2, drm/kms or others, but offer an alternative when you don't want/need to
use them for buffer allocation.
To keep a compatibility with what already exist allocated buffers are exported
in userland as dmabuf file descriptor (like ION is doing).

"Unix Device Memory Allocator" project [1] wants to create a userland library
which may allow to select, depending of the devices constraint, the best
back-end for allocation. With this RFC I would to propose to have common ioctl
for a maximum of allocators to avoid to duplicated back-ends for this library.

One of the issues that lead me to propose this RFC it is that since the beginning
it is a problem to allocate contiguous memory (CMA) without using v4l2 or
drm/kms so the first allocator available in this RFC use CMA memory.

An other question is: do we have others memory regions that could be interested
by this new framework ? I have in mind that some title memory regions could use
it or replace ION heaps (system, carveout, etc...).
Maybe it only solve CMA allocation issue, in this case there is no need to create
a new framework but only a dedicated ioctl.

Maybe the first thing to do is to change the name and the location of this
module, suggestions are welcome.

I have testing this code with the following program:

I'm still maintaining that we should just destage ION (with the todo items
fixed), since that is already an uabi to do this (afaiui at least), and
it's used on a few devices ... Please chat with Laura Abott.

(I thought I sent this before but apparently it didn't go through.
Apologies if this ends up as a repeat for anyone)

I've been reviewing this as well. Even if Ion is used on a number of
devices, the model is still a bit clunky. I was hoping to see if it
could be re-written from scratch in a framework like this and then
either add a shim layer or just coax all devices out there to actually
convert to the new framework.

I supposed another option is to destage as you suggested and work on
an improved version in parallel.