linux-kernel - Re: [PATCH 2/2] x86,mem-hotplug: modify PGD entry when removing memory

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Message-ID: <1403289003.25108.3.camel@misato.fc.hp.com>
Date:	Fri, 20 Jun 2014 12:30:03 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, tangchen@...fujitsu.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	guz.fnst@...fujitsu.com, zhangyanfei@...fujitsu.com
Subject: Re: [PATCH 2/2] x86,mem-hotplug: modify PGD entry when removing
 memory

On Wed, 2014-06-18 at 15:38 +0900, Yasuaki Ishimatsu wrote:
 :
> @@ -186,7 +186,12 @@ void sync_global_pgds(unsigned long start, unsigned long end)
>  		const pgd_t *pgd_ref = pgd_offset_k(address);
>  		struct page *page;
> 
> -		if (pgd_none(*pgd_ref))
> +		/*
> +		 * When it is called after memory hot remove, pgd_none()
> +		 * returns true. In this case (removed == 1), we must clear
> +		 * the PGD entries in the local PGD level page.
> +		 */
> +		if (pgd_none(*pgd_ref) && !removed)
>  			continue;
> 
>  		spin_lock(&pgd_lock);
> @@ -199,12 +204,18 @@ void sync_global_pgds(unsigned long start, unsigned long end)
>  			pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
>  			spin_lock(pgt_lock);
> 
> -			if (pgd_none(*pgd))
> -				set_pgd(pgd, *pgd_ref);
> -			else
> +			if (!pgd_none(*pgd_ref) && !pgd_none(*pgd))
>  				BUG_ON(pgd_page_vaddr(*pgd)
>  				       != pgd_page_vaddr(*pgd_ref));
> 
> +			if (removed) {

Shouldn't this condition be "else if"?

Thanks,
-Toshi

> +				if (pgd_none(*pgd_ref) && !pgd_none(*pgd))
> +					pgd_clear(pgd);
> +			} else {
> +				if (pgd_none(*pgd))
> +					set_pgd(pgd, *pgd_ref);
> +			}
> +
>  			spin_unlock(pgt_lock);
>  		}


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