linux-kernel - Re: [PATCH v2 2/3] resource: Add release_mem_region

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Date:	Wed, 10 Apr 2013 10:36:50 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	akpm@...ux-foundation.org, 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 2/3] resource: Add release_mem_region_adjustable()

On Tue, 2013-04-09 at 23:16 -0700, David Rientjes wrote:
> On Mon, 8 Apr 2013, Toshi Kani wrote:
> 
> > Added release_mem_region_adjustable(), which releases a requested
> > region from a currently busy memory resource.  This interface
> > adjusts the matched memory resource accordingly even if the
> > requested region does not match exactly but still fits into.
> > 
> > This new interface is intended for memory hot-delete.  During
> > bootup, memory resources are inserted from the boot descriptor
> > table, such as EFI Memory Table and e820.  Each memory resource
> > entry usually covers the whole contigous memory range.  Memory
> > 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.
> > 
> > There is no change to the existing interfaces since their restriction
> > is valid for I/O resources.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@...com>
> > Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> 
> Should this emit a warning for attempting to free a non-existant region 
> like __release_region() does?

Since __release_region() is a void function, it needs to emit a warning
within the func.  I made release_mem_region_adjustable() as an int
function so that the caller can receive an error and decide what to do
based on its operation.  I changed the caller __remove_pages() to emit a
warning message in PATCH 3/3 in this case.

> I think it would be better to base this off my patch and surround it with 
> #ifdef CONFIG_MEMORY_HOTREMOVE as suggested by Andrew.  There shouldn't be 
> any conflicts.

Yes, I realized that CONFIG_MEMORY_HOTREMOVE was a better choice, but I
had to use CONFIG_MEMORY_HOTPLUG at this time.  So, thanks for doing the
cleanup!

Since it's already rc6, I will keep my patchset independent for now.  I
will make minor change to update CONFIG_MEMORY_HOTPLUG to
CONFIG_MEMORY_HOTREMOVE after your patch gets accepted -- either by
sending a separate patch (if my patchset is already accepted) or
updating my current patchset (if my patchset is not accepted yet).

Thanks!
-Toshi

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