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From: Xishi Qiu <qiuxishi@huawei.com>
To: Andrea Reale <ar@linux.vnet.ibm.com>
Cc: Maciej Bielski <m.bielski@virtualopensystems.com>,
	<scott.branden@broadcom.com>, <will.deacon@arm.com>,
	<tech@virtualopensystems.com>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] Memory hotplug support for arm64 platform
Date: Fri, 16 Dec 2016 09:31:47 +0800	[thread overview]
Message-ID: <58534403.1040800@huawei.com> (raw)
In-Reply-To: <20161215183154.GC4806@samekh>

On 2016/12/16 2:31, Andrea Reale wrote:

> Hi Xishi Qiu,
> 
> thanks for your comments. 
> 
> The short anwser to your question is the following.  As you hinted,
> it is related to the way pfn_valid() is implemented in arm64 when
> CONFIG_HAVE_ARCH_PFN_VALID is true (default), i.e., just a check for
> the NOMAP flags on the corresponding memblocks.
> 
> Since arch_add_memory->__add_pages() expects pfn_valid() to return false
> when it is first called, we mark corresponding memory blocks with NOMAP;
> however, arch_add_memory->__add_pages()->__add_section()->__add_zone()
> expects pfn_valid() to return true when, at the end of its body,
> it cycles through pages to call SetPageReserved(). Since blocks are
> marked with NOMAP, pages will not be reserved there, henceforth we
> need to reserve them after we clear the NOMAP flag inside the body of
> arch_add_memory. Having pages reserved at the end of arch_add_memory
> is a preconditions for the upcoming onlining of memory blocks (see
> memory_block_change_state()).
> 
>> It's because that in memmap_init_zone() -> early_pfn_valid(), the new page is still
>> invalid, so we need to init it after memblock_clear_nomap()
>>
>> So why not use __init_single_page() and set_pageblock_migratetype()?
> 
> About your comment on memmap_init_zone()->early_pfn_valid(), I think
> that that particular check is never executed in the context of memory
> hotplug; in fact, just before the call to early_pfn_valid(), the code
> will jump to the `not_early` label, because the context == MEMMAP_HOPTLUG.
> 

Hi Andrea,

Thanks for your answer, I notice it now. I thought SetPageReserved() was
done in memmap_init_zone(), but the new kernel change this logic now, so
sorry for the noise.

Thanks,
Xishi Qiu

  reply	other threads:[~2016-12-16  1:33 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-14 12:16 Maciej Bielski
2016-12-15  6:18 ` Xishi Qiu
2016-12-15  6:40   ` Xishi Qiu
2016-12-15 18:31     ` Andrea Reale
2016-12-16  1:31       ` Xishi Qiu [this message]
2016-12-20 19:12 ` Scott Branden
2016-12-21  9:44   ` Maciej Bielski
2016-12-22  1:20     ` Scott Branden
2017-02-06 11:17       ` Andrea Reale
2017-02-08 20:08         ` Scott Branden
2017-03-30  0:40         ` Florian Fainelli
2017-03-31 14:16           ` Andrea Reale

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