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SubjectRe: [PATCH] resource: re-factor page_is_ram()
On 01.06.22 18:32, Vaibhav Jain wrote:
> Presently page_is_ram() relies on walk_system_ram_range() that performs a walk
> on kernel iomem resources hierarchy with a dummy callback __is_ram(). Before
> calling find_next_iomem_res(), walk_system_ram_range() does some book-keeping
> which can be avoided for page_is_ram() use-case.
>
> Hence this patch proposes to update page_is_ram() to directly call
> find_next_iomem_res() with minimal book-keeping needed.
>
> To avoid allocating a 'struct resource' the patch also updates
> find_next_iomem_res() to not return -EINVAL in case 'res == NULL'. Instead
> out 'struct resource *res' is only populated when its not NULL.
>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
> kernel/resource.c | 19 ++++++++-----------
> 1 file changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 34eaee179689..ecf6b9a50adc 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -311,7 +311,7 @@ EXPORT_SYMBOL(release_resource);
> *
> * If a resource is found, returns 0 and @*res is overwritten with the part
> * of the resource that's within [@start..@end]; if none is found, returns
> - * -ENODEV. Returns -EINVAL for invalid parameters.
> + * -ENODEV.
> *

There is still another -EINVAL in that function ...

> * @start: start address of the resource searched for
> * @end: end address of same resource
> @@ -328,9 +328,6 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
> {
> struct resource *p;
>
> - if (!res)
> - return -EINVAL;
> -
> if (start >= end)
> return -EINVAL;

As all callers guarantee that, we might just remove it.

>
> @@ -356,7 +353,7 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
> break;
> }
>
> - if (p) {
> + if (p && res) {
> /* copy data */
> *res = (struct resource) {
> .start = max(start, p->start),
> @@ -474,18 +471,18 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
> return ret;
> }
>
> -static int __is_ram(unsigned long pfn, unsigned long nr_pages, void *arg)
> -{
> - return 1;
> -}
> -
> /*
> * This generic page_is_ram() returns true if specified address is
> * registered as System RAM in iomem_resource list.
> */
> int __weak page_is_ram(unsigned long pfn)
> {
> - return walk_system_ram_range(pfn, 1, NULL, __is_ram) == 1;
> + const resource_size_t pfn_res = PFN_PHYS(pfn);
> +
> + return find_next_iomem_res(pfn_res,
> + pfn_res + 1,
> + IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY,
> + IORES_DESC_NONE, NULL) == 0;
> }
> EXPORT_SYMBOL_GPL(page_is_ram);
>

What about

a) A cleanup patch upfront that removes both -EINVAL cases from
find_next_iomem_res() followed by

b) The actual change to page_is_ram()

?

--
Thanks,

David / dhildenb

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