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SubjectRe: [PATCH v2] resource: Merge resources on a node when hot-adding memory
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On 08/06/2018 08:52 AM, Rashmica Gupta wrote:
> When hot-removing memory release_mem_region_adjustable() splits
> iomem resources if they are not the exact size of the memory being
> hot-deleted. Adding this memory back to the kernel adds a new
> resource.
>
> Eg a node has memory 0x0 - 0xfffffffff. Offlining and hot-removing
> 1GB from 0xf40000000 results in the single resource 0x0-0xfffffffff being
> split into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff.
>
> When we hot-add the memory back we now have three resources:
> 0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff.
>
> Now if we try to remove a section of memory that overlaps these resources,
> like 2GB from 0xf40000000, release_mem_region_adjustable() fails as it
> expects the chunk of memory to be within the boundaries of a single
> resource.

Hi,

it's the first time I see the resource code, so I might be easily wrong.
How can it happen that the second remove is section aligned but the
first one not?

> This patch adds a function request_resource_and_merge(). This is called
> instead of request_resource_conflict() when registering a resource in
> add_memory(). It calls request_resource_conflict() and if hot-removing is
> enabled (if it isn't we won't get resource fragmentation) we attempt to
> merge contiguous resources on the node.
>
> Signed-off-by: Rashmica Gupta <rashmica.g@gmail.com>
...
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
...
> +/*
> + * Attempt to merge resources on the node
> + */
> +static void merge_node_resources(int nid, struct resource *parent)
> +{
> + struct resource *res;
> + uint64_t start_addr;
> + uint64_t end_addr;
> + int ret;
> +
> + start_addr = node_start_pfn(nid) << PAGE_SHIFT;
> + end_addr = node_end_pfn(nid) << PAGE_SHIFT;
> +
> + write_lock(&resource_lock);
> +
> + /* Get the first resource */
> + res = parent->child;
> +
> + while (res) {
> + /* Check that the resource is within the node */
> + if (res->start < start_addr) {
> + res = res->sibling;
> + continue;
> + }
> + /* Exit if resource is past end of node */
> + if (res->sibling->end > end_addr)
> + break;

IIUC, resource end is closed, so adjacent resources's start is end+1.
But node_end_pfn is open, so the comparison above should use '>='
instead of '>'?

> +
> + ret = merge_resources(res);
> + if (!ret)
> + continue;
> + res = res->sibling;

Should this rather use next_resource() to merge at all levels of the
hierarchy? Although memory seems to be flat under &iomem_resource so it
would be just future-proofing.

Thanks,
Vlastimil

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