linux-kernel - Re: [Patch v4 09/12] memory-hotplug: remove page table of x86

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Date:	Fri, 07 Dec 2012 14:43:46 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Wen Congyang <wency@...fujitsu.com>
CC:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Jiang Liu <liuj97@...il.com>, Len Brown <len.brown@...el.com>,
	benh@...nel.crashing.org, paulus@...ba.org,
	Christoph Lameter <cl@...ux.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Jianguo Wu <wujianguo@...wei.com>,
	Jiang Liu <jiang.liu@...wei.com>
Subject: Re: [Patch v4 09/12] memory-hotplug: remove page table of x86_64
 architecture

On 11/27/2012 06:00 PM, Wen Congyang wrote:
> For hot removing memory, we sholud remove page table about the memory.
> So the patch searches a page table about the removed memory, and clear
> page table.

(snip)

> +void __meminit
> +kernel_physical_mapping_remove(unsigned long start, unsigned long end)
> +{
> +	unsigned long next;
> +	bool pgd_changed = false;
> +
> +	start = (unsigned long)__va(start);
> +	end = (unsigned long)__va(end);

Hi Wu,

Here, you expect start and end are physical addresses. But in
phys_xxx_remove() function, I think using virtual addresses is just
fine. Functions like pmd_addr_end() and pud_index() only calculate
an offset.

So, would you please tell me if we have to use physical addresses here ?

Thanks. :)

> +
> +	for (; start<  end; start = next) {
> +		pgd_t *pgd = pgd_offset_k(start);
> +		pud_t *pud;
> +
> +		next = pgd_addr_end(start, end);
> +
> +		if (!pgd_present(*pgd))
> +			continue;
> +
> +		pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
> +		phys_pud_remove(pud, __pa(start), __pa(next));
> +		if (free_pud_table(pud, pgd))
> +			pgd_changed = true;
> +		unmap_low_page(pud);
> +	}
> +
> +	if (pgd_changed)
> +		sync_global_pgds(start, end - 1);
> +
> +	flush_tlb_all();
> +}
> +
>   #ifdef CONFIG_MEMORY_HOTREMOVE
>   int __ref arch_remove_memory(u64 start, u64 size)
>   {
> @@ -692,6 +921,8 @@ int __ref arch_remove_memory(u64 start, u64 size)
>   	ret = __remove_pages(zone, start_pfn, nr_pages);
>   	WARN_ON_ONCE(ret);
>
> +	kernel_physical_mapping_remove(start, start + size);
> +
>   	return ret;
>   }
>   #endif


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