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

From: Simon Jeons <[email-masked]>
Date: Tue, 29 Jan 2013 21:27:05 -0600

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?

> 
> 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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