Re: [PATCH v3] resource: Merge resources on a node when hot-adding memory

From: Andrew Morton
Date: Thu Aug 09 2018 - 21:12:29 EST


On Thu, 9 Aug 2018 12:54:09 +1000 Rashmica Gupta <rashmica.g@xxxxxxxxx> 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 some 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.
>
> 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.

What is the end-user impact of this patch?

Do you believe the fix should be merged into 4.18? Backporting into
-stable kernels? If so, why?

Thanks.