linux-kernel - Re: [RFC PATCH] Memory hotplug support for arm64 platform

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Message-Id: <20170331141603.GA1440@samekh>
Date:   Fri, 31 Mar 2017 15:16:04 +0100
From:   Andrea Reale <ar@...ux.vnet.ibm.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Scott Branden <scott.branden@...adcom.com>,
        Maciej Bielski <m.bielski@...tualopensystems.com>,
        will.deacon@....com, linux-arm-kernel@...ts.infradead.org,
        qiuxishi@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Memory hotplug support for arm64 platform

Hi Florian,

thanks for your message. Please, find the replies in-line.

On Wed, Mar 29, 2017 at 05:40:02PM -0700, Florian Fainelli wrote:
> While the "hack" that sets/clears NOMAP in order for pfn_valid() to
> return false/true when appropriate during __add_pages() definitively
> does seem to work to probe the memory section, don't you also hit the
> same warning when you try to online that memory section in
> pages_correctly_reserved() once you have cleared the NOMAP flag?

Before arch_add_memory returns, we clear the nomap flag on the blocks,
so that pfn_valid will return true when executing on the corresponding
pages. This means that the condition in pages_correctly_reserved in
drivers/base/memory.c:

	if (WARN_ON_ONCE(!pfn_valid(pfn)))

will evaluate to false, so no warning should be issued, and the function
should continue to execute as expected.

Is it that you were referring to or did I miss the point?

> I will definitively give this a try on ARM64 since I need to get it
> working there.

Thanks a lot, any help in testing is really appreciated. 

> Do you mind posting a non-RFC patch?

We should release the hot-remove code that myself and Maciej have been
working on very soon (say, around one week); the plan is to rebase
everything and release hot-add and hot-remove as a single patch series
(including Scott's original patches and our hot-add patches). If you
can wait until then, we will probably minimize entropy; otherwise we
can also re-post the hot-add patches earlier and separately.

Thanks and regards,
Andrea