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

Jason Gunthorpe
2019-06-13T19:16:35Z

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@lst.de>
> 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@mellanox.com>

Jason