linux-kernel - Re: [PATCH] memory-hotplug: Clear pgdat which is allocated by bootmem in try_offline

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Date:	Tue, 21 Oct 2014 10:56:21 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, zhenzhang.zhang@...wei.com,
	wangnan0@...wei.com, tangchen@...fujitsu.com,
	dave.hansen@...el.com, rientjes@...gle.com
Subject: Re: [PATCH] memory-hotplug: Clear pgdat which is allocated by
 bootmem in try_offline_node()

On Mon, 2014-10-20 at 19:05 +0900, Yasuaki Ishimatsu wrote:
 :
> When hot removing memory, pgdat is set to 0 in try_offline_node().
> But if the pgdat is allocated by bootmem allocator, the clearing
> step is skipped. And when hot adding the same memory, the uninitialized
> pgdat is reused. But free_area_init_node() chacks wether pgdat is set

s/chacks/checks


> to zero. As a result, free_area_init_node() hits WARN_ON().
> 
> This patch clears pgdat which is allocated by bootmem allocator
> in try_offline_node().
> 
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> CC: Zhang Zhen <zhenzhang.zhang@...wei.com>
> CC: Wang Nan <wangnan0@...wei.com>
> CC: Tang Chen <tangchen@...fujitsu.com>
> CC: Toshi Kani <toshi.kani@...com>
> CC: Dave Hansen <dave.hansen@...el.com>
> CC: David Rientjes <rientjes@...gle.com>
> 
> ---
>  mm/memory_hotplug.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 29d8693..7649f7c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1943,7 +1943,7 @@ void try_offline_node(int nid)
> 
>  	if (!PageSlab(pgdat_page) && !PageCompound(pgdat_page))
>  		/* node data is allocated from boot memory */
> -		return;
> +		goto out;

Do we still need this if-statement?  That is, do we have to skip the
for-loop below even though it checks with is_vmalloc_addr()?

Thanks,
-Toshi


>  	/* free waittable in each zone */
>  	for (i = 0; i < MAX_NR_ZONES; i++) {
> @@ -1957,6 +1957,7 @@ void try_offline_node(int nid)
>  			vfree(zone->wait_table);
>  	}
> 
> +out:
>  	/*
>  	 * Since there is no way to guarentee the address of pgdat/zone is not
>  	 * on stack of any kernel threads or used by other kernel objects


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