Re: [PATCH 06/22] mm: factor out a devm_request_free_mem_region helper

[Jason Gunthorpe]

On Thu, Jun 13, 2019 at 11:43:09AM +0200, Christoph Hellwig wrote:
> Keep the physical address allocation that hmm_add_device does with the
> rest of the resource code, and allow future reuse of it without the hmm
> wrapper.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
>  include/linux/ioport.h |  2 ++
>  kernel/resource.c      | 39 +++++++++++++++++++++++++++++++++++++++
>  mm/hmm.c               | 33 ++++-----------------------------
>  3 files changed, 45 insertions(+), 29 deletions(-)
> 
> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> index da0ebaec25f0..76a33ae3bf6c 100644
> +++ b/include/linux/ioport.h
> @@ -286,6 +286,8 @@ static inline bool resource_overlaps(struct resource *r1, struct resource *r2)
>         return (r1->start <= r2->end && r1->end >= r2->start);
>  }
>  
> +struct resource *devm_request_free_mem_region(struct device *dev,
> +		struct resource *base, unsigned long size);
>  
>  #endif /* __ASSEMBLY__ */
>  #endif	/* _LINUX_IOPORT_H */
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 158f04ec1d4f..99c58134ed1c 100644
> +++ b/kernel/resource.c
> @@ -1628,6 +1628,45 @@ void resource_list_free(struct list_head *head)
>  }
>  EXPORT_SYMBOL(resource_list_free);
>  
> +#ifdef CONFIG_DEVICE_PRIVATE
> +/**
> + * devm_request_free_mem_region - find free region for device private memory
> + *
> + * @dev: device struct to bind the resource too
> + * @size: size in bytes of the device memory to add
> + * @base: resource tree to look in
> + *
> + * This function tries to find an empty range of physical address big enough to
> + * contain the new resource, so that it can later be hotpluged as ZONE_DEVICE
> + * memory, which in turn allocates struct pages.
> + */
> +struct resource *devm_request_free_mem_region(struct device *dev,
> +		struct resource *base, unsigned long size)
> +{
> +	resource_size_t end, addr;
> +	struct resource *res;
> +
> +	size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
> +	end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) - 1);

Even fixed it to use min_t

> +	addr = end - size + 1UL;
> +	for (; addr > size && addr >= base->start; addr -= size) {
> +		if (region_intersects(addr, size, 0, IORES_DESC_NONE) !=
> +				REGION_DISJOINT)
> +			continue;

The FIXME about the algorithm cost seems justified though, yikes.

> +
> +		res = devm_request_mem_region(dev, addr, size, dev_name(dev));
> +		if (!res)
> +			return ERR_PTR(-ENOMEM);
> +		res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;

I wonder if IORES_DESC_DEVICE_PRIVATE_MEMORY should be a function
argument?

Not really any substantive remark, so

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>

Jason