linux-kernel - Re: [PATCH v2 0/3] Support memory hot-delete to boot memory

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Date:	Mon, 8 Apr 2013 13:44:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxram@...ibm.com, guz.fnst@...fujitsu.com, tmac@...com,
	isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
	tangchen@...fujitsu.com, jiang.liu@...wei.com
Subject: Re: [PATCH v2 0/3] Support memory hot-delete to boot memory

On Mon,  8 Apr 2013 11:09:53 -0600 Toshi Kani <toshi.kani@...com> wrote:

> Memory hot-delete to a memory range present at boot causes an
> error message in __release_region(), such as:
> 
>  Trying to free nonexistent resource <0000000070000000-0000000077ffffff>
> 
> Hot-delete operation still continues since __release_region() is 
> a void function, but the target memory range is not freed from
> iomem_resource as the result.  This also leads a failure in a 
> subsequent hot-add operation to the same memory range since the
> address range is still in-use in iomem_resource.
> 
> This problem happens because the granularity of memory resource ranges
> may be different between boot and hot-delete.

So we don't need this new code if CONFIG_MEMORY_HOTPLUG=n?  If so, can
we please arrange for it to not be present if the user doesn't need it?

>  During bootup,
> iomem_resource is set up from the boot descriptor table, such as EFI
> Memory Table and e820.  Each resource entry usually covers the whole
> contiguous memory range.  Hot-delete request, on the other hand, may
> target to a particular range of memory resource, and its size can be
> much smaller than the whole contiguous memory.  Since the existing
> release interfaces like __release_region() require a requested region
> to be exactly matched to a resource entry, they do not allow a partial
> resource to be released.
> 
> This patchset introduces release_mem_region_adjustable() for memory
> hot-delete operations, which allows releasing a partial memory range
> and adjusts remaining resource accordingly.  This patchset makes no
> changes to the existing interfaces since their restriction is still
> valid for I/O resources.
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