linux-kernel - Re: [RFC PATCH v1] dma-buf: heaps: move the verification of heap

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Date: Tue, 4 Jun 2024 08:33:47 -0700
From: John Stultz <jstultz@...gle.com>
To: Hailong Liu <hailong.liu@...o.com>
Cc: Sumit Semwal <sumit.semwal@...aro.org>, 
	Benjamin Gaignard <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>, 
	"T.J. Mercier" <tjmercier@...gle.com>, Christian König <christian.koenig@....com>, 
	21cnbao@...il.com, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1] dma-buf: heaps: move the verification of
 heap_flags to the corresponding heap

On Mon, Jun 3, 2024 at 11:30 PM Hailong Liu <hailong.liu@...o.com> wrote:
> On 6/4/2024 2:06 AM, John Stultz wrote:
> > On Mon, Jun 3, 2024 at 10:21 AM Hailong Liu <hailong.liu@...o.com> wrote:
> >> We now aim to improve priority dma-buf allocation. Consider android
> >> animations scene:
> >>
> >> when device is in low memory, Allocating dma-buf as animation
> >> buffers enter direct_reclaimation, longer allocation time result in a
> >> laggy UI. But if we know the usage of the dma-buf, we can use some
> >> mechanisms to boost, e.g. animation-memory-pool.
> >
> > Can you generalize this a bit further? When would userland know to use
> > this new flag?
> > If it is aware, would it make sense to just use a separate heap name instead?
> >
> > (Also: These other mechanisms you mention should probably also be
> > submitted upstream, however for upstream there's also the requirement
> > that we have open users and are not just enabling proprietary blob
> > userspace, which makes any changes to dma-buf heaps for out of tree
> > code quite difficult)
> >
> >> However, dma-buf usage identification becomes a challenge. A potential
> >> solution could be heap_flags. the use of heap_flags seems ugly and
> >> contrary to the intended design as you said, How aboult extending
> >> dma_heap_allocation_data as follows?
> >>
> >> struct dma_heap_allocation_data {
> >>         __u64 len;
> >>         __u32 fd;
> >>         __u32 fd_flags;
> >>         __u64 heap_flags;
> >>         __u64 buf_flags: // buf usage
> >> };
> >
> > This would affect the ABI (forcing a new ioctl number).  And it's
> > unclear what flags you envision as buffer specific (rather than heap
> > specific as this patch suggested).
> >
> > I think we need more details about the specific problem you're seeing
> > and trying to resolve.
> This patch mainly focuses on optimization for Android scenarios. Let’s
> discuss it on the issue website.
> Bug: 344501512

Ok, we can do that if you need.

But if this is ever going to go upstream (and it's more and more
important that we minimize out of tree technical debt), conversations
about how to generalize this will need to happen on the list.

thanks
-john