linux-kernel - Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in remove

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Message-ID: <56134169.1070500@jp.fujitsu.com>
Date:	Tue, 6 Oct 2015 12:35:05 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Ishimatsu, Yasuaki/石松 靖章 
	<isimatu.yasuaki@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Waiman Long <waiman.long@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Izumi, Taku/泉 拓 
	<izumi.taku@...fujitsu.com>
Subject: Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in
 remove_pagetable()

On 2015/09/22 15:23, Ingo Molnar wrote:
> So when memory hotplug removes a piece of physical memory from pagetable
> mappings, it also frees the underlying PGD entry.
> 
> This complicates PGD management, so don't do this. We can keep the
> PGD mapped and the PUD table all clear - it's only a single 4K page
> per 512 GB of memory hotplugged.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Waiman Long <Waiman.Long@...com>
> Cc: linux-mm@...ck.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>

Ishimatsu-san, Tang-san, please check.

Doesn't this patch affects the issues of 
 5255e0a79fcc0ff47b387af92bd9ef5729b1b859
 9661d5bcd058fe15b4138a00d96bd36516134543

?

-Kame

> ---
>   arch/x86/mm/init_64.c | 27 ---------------------------
>   1 file changed, 27 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7129e7647a76..60b0cc3f2819 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -780,27 +780,6 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
>   	spin_unlock(&init_mm.page_table_lock);
>   }
>   
> -/* Return true if pgd is changed, otherwise return false. */
> -static bool __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd)
> -{
> -	pud_t *pud;
> -	int i;
> -
> -	for (i = 0; i < PTRS_PER_PUD; i++) {
> -		pud = pud_start + i;
> -		if (pud_val(*pud))
> -			return false;
> -	}
> -
> -	/* free a pud table */
> -	free_pagetable(pgd_page(*pgd), 0);
> -	spin_lock(&init_mm.page_table_lock);
> -	pgd_clear(pgd);
> -	spin_unlock(&init_mm.page_table_lock);
> -
> -	return true;
> -}
> -
>   static void __meminit
>   remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
>   		 bool direct)
> @@ -992,7 +971,6 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
>   	unsigned long addr;
>   	pgd_t *pgd;
>   	pud_t *pud;
> -	bool pgd_changed = false;
>   
>   	for (addr = start; addr < end; addr = next) {
>   		next = pgd_addr_end(addr, end);
> @@ -1003,13 +981,8 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
>   
>   		pud = (pud_t *)pgd_page_vaddr(*pgd);
>   		remove_pud_table(pud, addr, next, direct);
> -		if (free_pud_table(pud, pgd))
> -			pgd_changed = true;
>   	}
>   
> -	if (pgd_changed)
> -		sync_global_pgds(start, end - 1, 1);
> -
>   	flush_tlb_all();
>   }
>   
> 


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