linux-kernel - Re: Requirements to merge new heaps in the kernel

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Message-ID: <20241031-bouncy-cute-shrimp-cd2530@houat>
Date: Thu, 31 Oct 2024 17:45:23 +0100
From: Maxime Ripard <mripard@...hat.com>
To: metux <metux@....de>
Cc: Sumit Semwal <sumit.semwal@...aro.org>, 
	Benjamin Gaignard <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>, 
	John Stultz <jstultz@...gle.com>, "T.J. Mercier" <tjmercier@...gle.com>, 
	Christian König <christian.koenig@....com>, linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: Requirements to merge new heaps in the kernel

On Wed, Oct 30, 2024 at 12:16:22PM +0100, metux wrote:
> On 22.10.24 10:38, Maxime Ripard wrote:
> > I'm still interested in merging a carve-out driver[1], since it seems to be
> > in every vendor BSP and got asked again last week.
> > 
> > I remember from our discussion that for new heap types to be merged, we
> > needed a kernel use-case. Looking back, I'm not entirely sure how one
> > can provide that given that heaps are essentially facilities for
> > user-space.
> 
> For those who didn't follow your work, could you please give a short
> intro what's that all about ?
> 
> If I understand you correctly, you'd like the infrastructure of
> kmalloc() et al for things / memory regions that aren't the usual heap,
> right ?

No, not really. The discussion is about dma-buf heaps. They allow to
allocate buffers suitable for DMA from userspace. It might or might not
from the system memory, at the heap driver discretion.

> What's the practical use case ? GPU memory ? Shared memory between
> nodes in a multi-CPU / cluster machine ?
> 
> Is it related to NUMA ?

And since it's about DMA, it doesn't have much to do with CPUs either.

Maxime

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