linux-kernel - Re: [RFC] dma-buf: system_heap: add PTE

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Message-ID: <CAGsJ_4w-XtJ8zzc8H4OwW4XV21T8FWGxeoMnfAxmAgBhzrvxWQ@mail.gmail.com>
Date: Mon, 8 Dec 2025 17:52:52 +0800
From: Barry Song <21cnbao@...il.com>
To: gao xu <gaoxu2@...or.com>
Cc: "sumit.semwal@...aro.org" <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" <linux-media@...r.kernel.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "surenb@...gle.com" <surenb@...gle.com>, 
	zhouxiaolong <zhouxiaolong9@...or.com>, Ryan Roberts <ryan.roberts@....com>
Subject: Re: [RFC] dma-buf: system_heap: add PTE_CONT for larger contiguous

On Mon, Dec 8, 2025 at 5:41 PM gao xu <gaoxu2@...or.com> wrote:
>
> commit 04c7adb5871a ("dma-buf: system_heap: use larger contiguous mappings
> instead of per-page mmap") facilitates the use of PTE_CONT. The system_heap
> allocates pages of order 4 and 8 that meet the alignment requirements for
> PTE_CONT. enabling PTE_CONT for larger contiguous mappings.

Unfortunately, we don't have pte_cont for architectures other than
AArch64. On the other hand, AArch64 isn't automatically mapping
cont_pte for mmap. It might be better if this were done
automatically by the ARM code.

Ryan(Cced) is the expert on automatically setting cont_pte for
contiguous mapping, so let's ask for some advice from Ryan.

>
> After applying this patch, TLB misses are reduced by approximately 5% when
> opening the camera on Android systems.
>
> Signed-off-by: gao xu <gaoxu2@...or.com>
> ---

Thanks
Barry