Re: [PATCH 1/2] docs, xen/arm: Introduce reserved heap memory

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 24 Aug 2022, Henry Wang wrote:
> This commit introduces the reserved heap memory, which is parts of RAM
> reserved in the beginning of the boot time for heap.
> 
> A new boolean field `xen_heap` in `struct membank` is added to store the
> configuration telling if the memory bank is reserved as heap through
> `xen,static-mem` property in device tree `chosen` node.
> 
> Also, this commit introduces the logic to parse the reserved heap
> configuation in device tree by reusing the device tree entry definition
> of the static memory allocation feature:
> 
> - Add a boolean parameter `xen_heap` to `device_tree_get_meminfo` to
> reflect whether the memory bank is reserved as heap.
> 
> - Use `device_tree_get_meminfo` to parse the reserved heap configuation
> in `chosen` node of the device tree.
> 
> - In order to reuse the function `device_tree_get_meminfo`, the
> return type of `process_chosen_node` is changed from void to int.
> 
> A documentation section is added, describing the definition of reserved
> heap memory and the method of enabling the reserved heap memory through
> device tree at boot time.
> 
> Signed-off-by: Henry Wang <Henry.Wang@xxxxxxx>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> ---
> The name of the device tree property was chosen because we want to
> reuse as much as the device tree parsing helpers from the static
> memory allocation feature, but we would like to hear the upstream
> reviewers' opinion about if using "xen,static-heap" is better.
> ---
> Changes from RFC to v1:
> - Rename the terminology to reserved heap.
> ---
>  docs/misc/arm/device-tree/booting.txt | 46 +++++++++++++++++++++++++
>  xen/arch/arm/bootfdt.c                | 49 +++++++++++++++++++++------
>  xen/arch/arm/domain_build.c           |  5 +--
>  xen/arch/arm/include/asm/setup.h      |  1 +
>  4 files changed, 89 insertions(+), 12 deletions(-)
> 
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index 98253414b8..e064f64d9a 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -378,3 +378,49 @@ device-tree:
>  
>  This will reserve a 512MB region starting at the host physical address
>  0x30000000 to be exclusively used by DomU1.
> +
> +
> +Reserved Heap Memory
> +====================
> +
> +The reserved heap memory (also known as the statically-configured heap) 
> refers
> +to parts of RAM reserved in the beginning for heap. The memory is reserved by
> +configuration in the device tree using physical address ranges.
> +
> +The reserved heap memory declared in the device tree defines the memory areas
> +that will be reserved to be used exclusively as heap.
> +
> +- For Arm32, since there can be seperated heaps, the reserved heap will be 
> used
> +for both domheap and xenheap.
> +- For Arm64, since domheap and xenheap are the same, the defined reserved 
> heap
> +areas shall always go to the heap allocator.
> +
> +The reserved heap memory is an optional feature and can be enabled by adding 
> a
> +device tree property in the `chosen` node. Currently, this feature reuses the
> +static memory allocation device tree configuration.
> +
> +The dtb property should look like as follows:
> +
> +- property name
> +
> +    "xen,static-mem" (Should be used in the `chosen` node)
> +
> +- cells
> +
> +    Specify the start address and the length of the reserved heap memory.
> +    The number of cells for the address and the size should be defined
> +    using the properties `#xen,static-mem-address-cells` and
> +    `#xen,static-mem-size-cells` respectively.

I would choose a different name for the property not to be confused with
a domain's xen,static-mem property which is for a different purpose: the
memory of the domain.

---

- xen,static-heap

    Property under the top-level "chosen" node. It specifies the address
    and size of Xen reserved heap memory.


- #xen,static-heap-address-cells and #xen,static-heap-size-cells

    Specify the number of cells used for the address and size of the
    xen,static-heap property under "chosen".

---