Subject: Re: [PATCH v6 08/15] memory-hotplug: Common APIs to support page tables hot-remove

From: Simon Jeons <[email-masked]>
Date: Wed, 30 Jan 2013 01:32:58 -0600

On Wed, 2013-01-30 at 13:55 +0800, Tang Chen wrote:
> On 01/30/2013 11:27 AM, Simon Jeons wrote:
> > On Wed, 2013-01-30 at 10:16 +0800, Tang Chen wrote:
> >> On 01/29/2013 09:04 PM, Simon Jeons wrote:
> >>> Hi Tang,
> >>> On Wed, 2013-01-09 at 17:32 +0800, Tang Chen wrote:
> >>>> From: Wen Congyang<[email-masked]>
> >>>>
> >>>> When memory is removed, the corresponding pagetables should alse be removed.
> >>>> This patch introduces some common APIs to support vmemmap pagetable and x86_64
> >>>> architecture pagetable removing.
> >>>
> >>> Why don't need to build_all_zonelists like online_pages does during
> >>> hot-add path(add_memory)?
> >>
> >> Hi Simon,
> >>
> >> As you said, build_all_zonelists is done by online_pages. When the
> >> memory device
> >> is hot-added, we cannot use it. we can only use is when we online the
> >> pages on it.
> >
> > Why?
> >
> > If a node has just one memory device and memory is small, some zone will
> > not present like zone_highmem, then hot-add another memory device and
> > zone_highmem appear, if you should build_all_zonelists this time?
> 
> Hi Simon,
> 
> We built zone list when the first memory on the node is hot-added.
> 
> add_memory()
>   |-->if (!node_online(nid)) hotadd_new_pgdat()
>                               |-->free_area_init_node()
>                               |-->build_all_zonelists()
> 
> All the zones on the new node will be initialized as empty. So here, we 
> build zone list.
> 
> But actually we did nothing because no page is online, and zones are empty.
> In build_zonelists_node(), populated_zone(zone) will always be false.
> 
> The real work of building zone list is when pages are online. :)
> 
> 
> And in your question, you said some small memory is there, and 
> zone_normal is present.
> OK, when these pages are onlined (not added), the zone list has been 
> rebuilt.
> But pages in zone_highmem is not added, which means not onlined, so we 
> don't need to
> build zone list for it. And later, the zone_highmem pages are added, we 
> still don't
> rebuild the zone list because the real rebuilding work is when the pages 
> are onlined.
> 
> I think this is the current logic. :)

Thanks for you clarify. Actually, I miss "Even if the memory is
hot-added, it is not at ready-to-use state. For using newly added
memory, you have to 'online' the memory section" in the doc. :)

> 
> Thanks. :)
> 
> >
> >>
> >> But we can online the pages as different types, kernel or movable (which
> >> belongs to
> >> different zones), and we can online part of the memory, not all of them.
> >> So each time we online some pages, we should check if we need to update
> >> the zone list.
> >>
> >> So I think that is why we do build_all_zonelists when online_pages.
> >> (just my opinion)
> >>
> >> Thanks. :)
> >>
> >>>
> >>>>
> >>>> All pages of virtual mapping in removed memory cannot be freedi if some pages
> >>>> used as PGD/PUD includes not only removed memory but also other memory. So the
> >>>> patch uses the following way to check whether page can be freed or not.
> >>>>
> >>>>    1. When removing memory, the page structs of the revmoved memory are filled
> >>>>       with 0FD.
> >>>>    2. All page structs are filled with 0xFD on PT/PMD, PT/PMD can be cleared.
> >>>>       In this case, the page used as PT/PMD can be freed.
> >>>>
> >>>> Signed-off-by: Yasuaki Ishimatsu<[email-masked]>
> >>>> Signed-off-by: Jianguo Wu<[email-masked]>
> >>>> Signed-off-by: Wen Congyang<[email-masked]>
> >>>> Signed-off-by: Tang Chen<[email-masked]>
> >>>> ---
> >>>>    arch/x86/include/asm/pgtable_types.h |    1 +
> >>>>    arch/x86/mm/init_64.c                |  299 ++++++++++++++++++++++++++++++++++
> >>>>    arch/x86/mm/pageattr.c               |   47 +++---
> >>>>    include/linux/bootmem.h              |    1 +
> >>>>    4 files changed, 326 insertions(+), 22 deletions(-)
> >>>>
> >>>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> >>>> index 3c32db8..4b6fd2a 100644
> >>>> --- a/arch/x86/include/asm/pgtable_types.h
> >>>> +++ b/arch/x86/include/asm/pgtable_types.h
> >>>> @@ -352,6 +352,7 @@ static inline void update_page_count(int level, unsigned long pages) { }
> >>>>     * as a pte too.
> >>>>     */
> >>>>    extern pte_t *lookup_address(unsigned long address, unsigned int *level);
> >>>> +extern int __split_large_page(pte_t *kpte, unsigned long address, pte_t *pbase);
> >>>>
> >>>>    #endif	/* !__ASSEMBLY__ */
> >>>>
> >>>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> >>>> index 9ac1723..fe01116 100644
> >>>> --- a/arch/x86/mm/init_64.c
> >>>> +++ b/arch/x86/mm/init_64.c
> >>>> @@ -682,6 +682,305 @@ int arch_add_memory(int nid, u64 start, u64 size)
> >>>>    }
> >>>>    EXPORT_SYMBOL_GPL(arch_add_memory);
> >>>>
> >>>> +#define PAGE_INUSE 0xFD
> >>>> +
> >>>> +static void __meminit free_pagetable(struct page *page, int order)
> >>>> +{
> >>>> +	struct zone *zone;
> >>>> +	bool bootmem = false;
> >>>> +	unsigned long magic;
> >>>> +	unsigned int nr_pages = 1<<   order;
> >>>> +
> >>>> +	/* bootmem page has reserved flag */
> >>>> +	if (PageReserved(page)) {
> >>>> +		__ClearPageReserved(page);
> >>>> +		bootmem = true;
> >>>> +
> >>>> +		magic = (unsigned long)page->lru.next;
> >>>> +		if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
> >>>> +			while (nr_pages--)
> >>>> +				put_page_bootmem(page++);
> >>>> +		} else
> >>>> +			__free_pages_bootmem(page, order);
> >>>> +	} else
> >>>> +		free_pages((unsigned long)page_address(page), order);
> >>>> +
> >>>> +	/*
> >>>> +	 * SECTION_INFO pages and MIX_SECTION_INFO pages
> >>>> +	 * are all allocated by bootmem.
> >>>> +	 */
> >>>> +	if (bootmem) {
> >>>> +		zone = page_zone(page);
> >>>> +		zone_span_writelock(zone);
> >>>> +		zone->present_pages += nr_pages;
> >>>> +		zone_span_writeunlock(zone);
> >>>> +		totalram_pages += nr_pages;
> >>>> +	}
> >>>> +}
> >>>> +
> >>>> +static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
> >>>> +{
> >>>> +	pte_t *pte;
> >>>> +	int i;
> >>>> +
> >>>> +	for (i = 0; i<   PTRS_PER_PTE; i++) {
> >>>> +		pte = pte_start + i;
> >>>> +		if (pte_val(*pte))
> >>>> +			return;
> >>>> +	}
> >>>> +
> >>>> +	/* free a pte talbe */
> >>>> +	free_pagetable(pmd_page(*pmd), 0);
> >>>> +	spin_lock(&init_mm.page_table_lock);
> >>>> +	pmd_clear(pmd);
> >>>> +	spin_unlock(&init_mm.page_table_lock);
> >>>> +}
> >>>> +
> >>>> +static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> >>>> +{
> >>>> +	pmd_t *pmd;
> >>>> +	int i;
> >>>> +
> >>>> +	for (i = 0; i<   PTRS_PER_PMD; i++) {
> >>>> +		pmd = pmd_start + i;
> >>>> +		if (pmd_val(*pmd))
> >>>> +			return;
> >>>> +	}
> >>>> +
> >>>> +	/* free a pmd talbe */
> >>>> +	free_pagetable(pud_page(*pud), 0);
> >>>> +	spin_lock(&init_mm.page_table_lock);
> >>>> +	pud_clear(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)
> >>>> +{
> >>>> +	unsigned long next, pages = 0;
> >>>> +	pte_t *pte;
> >>>> +	void *page_addr;
> >>>> +	phys_addr_t phys_addr;
> >>>> +
> >>>> +	pte = pte_start + pte_index(addr);
> >>>> +	for (; addr<   end; addr = next, pte++) {
> >>>> +		next = (addr + PAGE_SIZE)&   PAGE_MASK;
> >>>> +		if (next>   end)
> >>>> +			next = end;
> >>>> +
> >>>> +		if (!pte_present(*pte))
> >>>> +			continue;
> >>>> +
> >>>> +		/*
> >>>> +		 * We mapped [0,1G) memory as identity mapping when
> >>>> +		 * initializing, in arch/x86/kernel/head_64.S. These
> >>>> +		 * pagetables cannot be removed.
> >>>> +		 */
> >>>> +		phys_addr = pte_val(*pte) + (addr&   PAGE_MASK);
> >>>> +		if (phys_addr<   (phys_addr_t)0x40000000)
> >>>> +			return;
> >>>> +
> >>>> +		if (IS_ALIGNED(addr, PAGE_SIZE)&&
> >>>> +		    IS_ALIGNED(next, PAGE_SIZE)) {
> >>>> +			if (!direct) {
> >>>> +				free_pagetable(pte_page(*pte), 0);
> >>>> +				pages++;
> >>>> +			}
> >>>> +
> >>>> +			spin_lock(&init_mm.page_table_lock);
> >>>> +			pte_clear(&init_mm, addr, pte);
> >>>> +			spin_unlock(&init_mm.page_table_lock);
> >>>> +		} else {
> >>>> +			/*
> >>>> +			 * If we are not removing the whole page, it means
> >>>> +			 * other ptes in this page are being used and we canot
> >>>> +			 * remove them. So fill the unused ptes with 0xFD, and
> >>>> +			 * remove the page when it is wholly filled with 0xFD.
> >>>> +			 */
> >>>> +			memset((void *)addr, PAGE_INUSE, next - addr);
> >>>> +			page_addr = page_address(pte_page(*pte));
> >>>> +
> >>>> +			if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) {
> >>>> +				free_pagetable(pte_page(*pte), 0);
> >>>> +				pages++;
> >>>> +
> >>>> +				spin_lock(&init_mm.page_table_lock);
> >>>> +				pte_clear(&init_mm, addr, pte);
> >>>> +				spin_unlock(&init_mm.page_table_lock);
> >>>> +			}
> >>>> +		}
> >>>> +	}
> >>>> +
> >>>> +	/* Call free_pte_table() in remove_pmd_table(). */
> >>>> +	flush_tlb_all();
> >>>> +	if (direct)
> >>>> +		update_page_count(PG_LEVEL_4K, -pages);
> >>>> +}
> >>>> +
> >>>> +static void __meminit
> >>>> +remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> >>>> +		 bool direct)
> >>>> +{
> >>>> +	unsigned long pte_phys, next, pages = 0;
> >>>> +	pte_t *pte_base;
> >>>> +	pmd_t *pmd;
> >>>> +
> >>>> +	pmd = pmd_start + pmd_index(addr);
> >>>> +	for (; addr<   end; addr = next, pmd++) {
> >>>> +		next = pmd_addr_end(addr, end);
> >>>> +
> >>>> +		if (!pmd_present(*pmd))
> >>>> +			continue;
> >>>> +
> >>>> +		if (pmd_large(*pmd)) {
> >>>> +			if (IS_ALIGNED(addr, PMD_SIZE)&&
> >>>> +			    IS_ALIGNED(next, PMD_SIZE)) {
> >>>> +				if (!direct) {
> >>>> +					free_pagetable(pmd_page(*pmd),
> >>>> +						       get_order(PMD_SIZE));
> >>>> +					pages++;
> >>>> +				}
> >>>> +
> >>>> +				spin_lock(&init_mm.page_table_lock);
> >>>> +				pmd_clear(pmd);
> >>>> +				spin_unlock(&init_mm.page_table_lock);
> >>>> +				continue;
> >>>> +			}
> >>>> +
> >>>> +			/*
> >>>> +			 * We use 2M page, but we need to remove part of them,
> >>>> +			 * so split 2M page to 4K page.
> >>>> +			 */
> >>>> +			pte_base = (pte_t *)alloc_low_page(&pte_phys);
> >>>> +			BUG_ON(!pte_base);
> >>>> +			__split_large_page((pte_t *)pmd, addr,
> >>>> +					   (pte_t *)pte_base);
> >>>> +
> >>>> +			spin_lock(&init_mm.page_table_lock);
> >>>> +			pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
> >>>> +			spin_unlock(&init_mm.page_table_lock);
> >>>> +
> >>>> +			flush_tlb_all();
> >>>> +		}
> >>>> +
> >>>> +		pte_base = (pte_t *)map_low_page((pte_t *)pmd_page_vaddr(*pmd));
> >>>> +		remove_pte_table(pte_base, addr, next, direct);
> >>>> +		free_pte_table(pte_base, pmd);
> >>>> +		unmap_low_page(pte_base);
> >>>> +	}
> >>>> +
> >>>> +	/* Call free_pmd_table() in remove_pud_table(). */
> >>>> +	if (direct)
> >>>> +		update_page_count(PG_LEVEL_2M, -pages);
> >>>> +}
> >>>> +
> >>>> +static void __meminit
> >>>> +remove_pud_table(pud_t *pud_start, unsigned long addr, unsigned long end,
> >>>> +		 bool direct)
> >>>> +{
> >>>> +	unsigned long pmd_phys, next, pages = 0;
> >>>> +	pmd_t *pmd_base;
> >>>> +	pud_t *pud;
> >>>> +
> >>>> +	pud = pud_start + pud_index(addr);
> >>>> +	for (; addr<   end; addr = next, pud++) {
> >>>> +		next = pud_addr_end(addr, end);
> >>>> +
> >>>> +		if (!pud_present(*pud))
> >>>> +			continue;
> >>>> +
> >>>> +		if (pud_large(*pud)) {
> >>>> +			if (IS_ALIGNED(addr, PUD_SIZE)&&
> >>>> +			    IS_ALIGNED(next, PUD_SIZE)) {
> >>>> +				if (!direct) {
> >>>> +					free_pagetable(pud_page(*pud),
> >>>> +						       get_order(PUD_SIZE));
> >>>> +					pages++;
> >>>> +				}
> >>>> +
> >>>> +				spin_lock(&init_mm.page_table_lock);
> >>>> +				pud_clear(pud);
> >>>> +				spin_unlock(&init_mm.page_table_lock);
> >>>> +				continue;
> >>>> +			}
> >>>> +
> >>>> +			/*
> >>>> +			 * We use 1G page, but we need to remove part of them,
> >>>> +			 * so split 1G page to 2M page.
> >>>> +			 */
> >>>> +			pmd_base = (pmd_t *)alloc_low_page(&pmd_phys);
> >>>> +			BUG_ON(!pmd_base);
> >>>> +			__split_large_page((pte_t *)pud, addr,
> >>>> +					   (pte_t *)pmd_base);
> >>>> +
> >>>> +			spin_lock(&init_mm.page_table_lock);
> >>>> +			pud_populate(&init_mm, pud, __va(pmd_phys));
> >>>> +			spin_unlock(&init_mm.page_table_lock);
> >>>> +
> >>>> +			flush_tlb_all();
> >>>> +		}
> >>>> +
> >>>> +		pmd_base = (pmd_t *)map_low_page((pmd_t *)pud_page_vaddr(*pud));
> >>>> +		remove_pmd_table(pmd_base, addr, next, direct);
> >>>> +		free_pmd_table(pmd_base, pud);
> >>>> +		unmap_low_page(pmd_base);
> >>>> +	}
> >>>> +
> >>>> +	if (direct)
> >>>> +		update_page_count(PG_LEVEL_1G, -pages);
> >>>> +}
> >>>> +
> >>>> +/* start and end are both virtual address. */
> >>>> +static void __meminit
> >>>> +remove_pagetable(unsigned long start, unsigned long end, bool direct)
> >>>> +{
> >>>> +	unsigned long next;
> >>>> +	pgd_t *pgd;
> >>>> +	pud_t *pud;
> >>>> +	bool pgd_changed = false;
> >>>> +
> >>>> +	for (; start<   end; start = next) {
> >>>> +		pgd = pgd_offset_k(start);
> >>>> +		if (!pgd_present(*pgd))
> >>>> +			continue;
> >>>> +
> >>>> +		next = pgd_addr_end(start, end);
> >>>> +
> >>>> +		pud = (pud_t *)map_low_page((pud_t *)pgd_page_vaddr(*pgd));
> >>>> +		remove_pud_table(pud, start, next, direct);
> >>>> +		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)
> >>>>    {
> >>>> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> >>>> index a718e0d..7dcb6f9 100644
> >>>> --- a/arch/x86/mm/pageattr.c
> >>>> +++ b/arch/x86/mm/pageattr.c
> >>>> @@ -501,21 +501,13 @@ out_unlock:
> >>>>    	return do_split;
> >>>>    }
> >>>>
> >>>> -static int split_large_page(pte_t *kpte, unsigned long address)
> >>>> +int __split_large_page(pte_t *kpte, unsigned long address, pte_t *pbase)
> >>>>    {
> >>>>    	unsigned long pfn, pfninc = 1;
> >>>>    	unsigned int i, level;
> >>>> -	pte_t *pbase, *tmp;
> >>>> +	pte_t *tmp;
> >>>>    	pgprot_t ref_prot;
> >>>> -	struct page *base;
> >>>> -
> >>>> -	if (!debug_pagealloc)
> >>>> -		spin_unlock(&cpa_lock);
> >>>> -	base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
> >>>> -	if (!debug_pagealloc)
> >>>> -		spin_lock(&cpa_lock);
> >>>> -	if (!base)
> >>>> -		return -ENOMEM;
> >>>> +	struct page *base = virt_to_page(pbase);
> >>>>
> >>>>    	spin_lock(&pgd_lock);
> >>>>    	/*
> >>>> @@ -523,10 +515,11 @@ static int split_large_page(pte_t *kpte, unsigned long address)
> >>>>    	 * up for us already:
> >>>>    	 */
> >>>>    	tmp = lookup_address(address,&level);
> >>>> -	if (tmp != kpte)
> >>>> -		goto out_unlock;
> >>>> +	if (tmp != kpte) {
> >>>> +		spin_unlock(&pgd_lock);
> >>>> +		return 1;
> >>>> +	}
> >>>>
> >>>> -	pbase = (pte_t *)page_address(base);
> >>>>    	paravirt_alloc_pte(&init_mm, page_to_pfn(base));
> >>>>    	ref_prot = pte_pgprot(pte_clrhuge(*kpte));
> >>>>    	/*
> >>>> @@ -579,17 +572,27 @@ static int split_large_page(pte_t *kpte, unsigned long address)
> >>>>    	 * going on.
> >>>>    	 */
> >>>>    	__flush_tlb_all();
> >>>> +	spin_unlock(&pgd_lock);
> >>>>
> >>>> -	base = NULL;
> >>>> +	return 0;
> >>>> +}
> >>>>
> >>>> -out_unlock:
> >>>> -	/*
> >>>> -	 * If we dropped out via the lookup_address check under
> >>>> -	 * pgd_lock then stick the page back into the pool:
> >>>> -	 */
> >>>> -	if (base)
> >>>> +static int split_large_page(pte_t *kpte, unsigned long address)
> >>>> +{
> >>>> +	pte_t *pbase;
> >>>> +	struct page *base;
> >>>> +
> >>>> +	if (!debug_pagealloc)
> >>>> +		spin_unlock(&cpa_lock);
> >>>> +	base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
> >>>> +	if (!debug_pagealloc)
> >>>> +		spin_lock(&cpa_lock);
> >>>> +	if (!base)
> >>>> +		return -ENOMEM;
> >>>> +
> >>>> +	pbase = (pte_t *)page_address(base);
> >>>> +	if (__split_large_page(kpte, address, pbase))
> >>>>    		__free_page(base);
> >>>> -	spin_unlock(&pgd_lock);
> >>>>
> >>>>    	return 0;
> >>>>    }
> >>>> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> >>>> index 3f778c2..190ff06 100644
> >>>> --- a/include/linux/bootmem.h
> >>>> +++ b/include/linux/bootmem.h
> >>>> @@ -53,6 +53,7 @@ extern void free_bootmem_node(pg_data_t *pgdat,
> >>>>    			      unsigned long size);
> >>>>    extern void free_bootmem(unsigned long physaddr, unsigned long size);
> >>>>    extern void free_bootmem_late(unsigned long physaddr, unsigned long size);
> >>>> +extern void __free_pages_bootmem(struct page *page, unsigned int order);
> >>>>
> >>>>    /*
> >>>>     * Flags for reserve_bootmem (also if CONFIG_HAVE_ARCH_BOOTMEM_NODE,
> >>>
> >>>
> >>> --
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> >>>
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to [email-masked].  For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email:<a href=mailto:"[email-masked]">  [email-masked]</a>
> >
> >
> >
> 
> --
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