Re: [Patch v4 08/12] memory-hotplug: remove memmap of sparse-vmemmap

Yasuaki Ishimatsu
2012-11-30T02:55:39Z

Hi Jianguo,

2012/11/30 11:47, Jianguo Wu wrote:
> Hi Congyang,
>
> Thanks for your review and comments.
>
> On 2012/11/30 9:45, Wen Congyang wrote:
>
>> At 11/28/2012 05:40 PM, Jianguo Wu Wrote:
>>> Hi Congyang,
>>>
>>> I think vmemmap's pgtable pages should be freed after all entries are cleared, I have a patch to do this.
>>> The code logic is the same as [Patch v4 09/12] memory-hotplug: remove page table of x86_64 architecture.
>>>
>>> How do you think about this?
>>>
>>> Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
>>> Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
>>> ---
>>> include/linux/mm.h | 1 +
>>> mm/sparse-vmemmap.c | 214 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>> mm/sparse.c | 5 +-
>>> 3 files changed, 218 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 5657670..1f26af5 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -1642,6 +1642,7 @@ int vmemmap_populate(struct page *start_page, unsigned long pages, int node);
>>> void vmemmap_populate_print_last(void);
>>> void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
>>> unsigned long size);
>>> +void vmemmap_free(struct page *memmap, unsigned long nr_pages);
>>>
>>> enum mf_flags {
>>> MF_COUNT_INCREASED = 1 << 0,
>>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>>> index 1b7e22a..242cb28 100644
>>> --- a/mm/sparse-vmemmap.c
>>> +++ b/mm/sparse-vmemmap.c
>>> @@ -29,6 +29,10 @@
>>> #include <asm/pgalloc.h>
>>> #include <asm/pgtable.h>
>>>
>>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>>> +#include <asm/tlbflush.h>
>>> +#endif
>>> +
>>> /*
>>> * Allocate a block of memory to be used to back the virtual memory map
>>> * or to back the page tables that are used to create the mapping.
>>> @@ -224,3 +228,213 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
>>> vmemmap_buf_end = NULL;
>>> }
>>> }
>>> +
>>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>>> +static void vmemmap_free_pages(struct page *page, int order)
>>> +{
>>> + struct zone *zone;
>>> + unsigned long magic;
>>> +
>>> + magic = (unsigned long) page->lru.next;
>>> + if (magic = SECTION_INFO || magic = MIX_SECTION_INFO) {
>>> + put_page_bootmem(page);
>>> +
>>> + zone = page_zone(page);
>>> + zone_span_writelock(zone);
>>> + zone->present_pages++;
>>> + zone_span_writeunlock(zone);
>>> + totalram_pages++;
>>> + } else {
>>> + if (is_vmalloc_addr(page_address(page)))
>>> + vfree(page_address(page));
>>
>> Hmm, vmemmap doesn't use vmalloc() to allocate memory.
>>
>
> yes, this can be removed.
>
>>> + else
>>> + free_pages((unsigned long)page_address(page), order);
>>> + }
>>> +}
>>> +
>>> +static void free_pte_table(pmd_t *pmd)
>>> +{
>>> + pte_t *pte, *pte_start;
>>> + int i;
>>> +
>>> + pte_start = (pte_t *)pmd_page_vaddr(*pmd);
>>> + for (i = 0; i < PTRS_PER_PTE; i++) {
>>> + pte = pte_start + i;
>>> + if (pte_val(*pte))
>>> + return;
>>> + }
>>> +
>>> + /* free a pte talbe */
>>> + vmemmap_free_pages(pmd_page(*pmd), 0);
>>> + spin_lock(&init_mm.page_table_lock);
>>> + pmd_clear(pmd);
>>> + spin_unlock(&init_mm.page_table_lock);
>>> +}
>>> +
>>> +static void free_pmd_table(pud_t *pud)
>>> +{
>>> + pmd_t *pmd, *pmd_start;
>>> + int i;
>>> +
>>> + pmd_start = (pmd_t *)pud_page_vaddr(*pud);
>>> + for (i = 0; i < PTRS_PER_PMD; i++) {
>>> + pmd = pmd_start + i;
>>> + if (pmd_val(*pmd))
>>> + return;
>>> + }
>>> +
>>> + /* free a pmd talbe */
>>> + vmemmap_free_pages(pud_page(*pud), 0);
>>> + spin_lock(&init_mm.page_table_lock);
>>> + pud_clear(pud);
>>> + spin_unlock(&init_mm.page_table_lock);
>>> +}
>>> +
>>> +static void free_pud_table(pgd_t *pgd)
>>> +{
>>> + pud_t *pud, *pud_start;
>>> + int i;
>>> +
>>> + pud_start = (pud_t *)pgd_page_vaddr(*pgd);
>>> + for (i = 0; i < PTRS_PER_PUD; i++) {
>>> + pud = pud_start + i;
>>> + if (pud_val(*pud))
>>> + return;
>>> + }
>>> +
>>> + /* free a pud table */
>>> + vmemmap_free_pages(pgd_page(*pgd), 0);
>>> + spin_lock(&init_mm.page_table_lock);
>>> + pgd_clear(pgd);
>>> + spin_unlock(&init_mm.page_table_lock);
>>> +}
>>> +
>>> +static int split_large_page(pte_t *kpte, unsigned long address, pte_t *pbase)
>>> +{
>>> + struct page *page = pmd_page(*(pmd_t *)kpte);
>>> + int i = 0;
>>> + unsigned long magic;
>>> + unsigned long section_nr;
>>> +
>>> + __split_large_page(kpte, address, pbase);
>>> + __flush_tlb_all();
>>> +
>>> + magic = (unsigned long) page->lru.next;
>>> + if (magic = SECTION_INFO) {
>>> + section_nr = pfn_to_section_nr(page_to_pfn(page));
>>> + while (i < PTRS_PER_PMD) {
>>> + page++;
>>> + i++;
>>> + get_page_bootmem(section_nr, page, SECTION_INFO);
>>> + }
>>> + }
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +static void vmemmap_pte_remove(pmd_t *pmd, unsigned long addr, unsigned long end)
>>> +{
>>> + pte_t *pte;
>>> + unsigned long next;
>>> +
>>> + pte = pte_offset_kernel(pmd, addr);
>>> + for (; addr < end; pte++, addr += PAGE_SIZE) {
>>> + next = (addr + PAGE_SIZE) & PAGE_MASK;
>>> + if (next > end)
>>> + next = end;
>>> +
>>> + if (pte_none(*pte))
>>> + continue;
>>> + if (IS_ALIGNED(addr, PAGE_SIZE) &&
>>> + IS_ALIGNED(end, PAGE_SIZE)) {
>>> + vmemmap_free_pages(pte_page(*pte), 0);
>>> + spin_lock(&init_mm.page_table_lock);
>>> + pte_clear(&init_mm, addr, pte);
>>> + spin_unlock(&init_mm.page_table_lock);
>>
>> If addr or end is not alianed with PAGE_SIZE, you may leak some
>> memory.
>>
>
> yes, I think we can handle this situation with the method you mentioned in the change log:
> 1. When removing memory, the page structs of the revmoved memory are filled
> with 0xFD.
> 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.
>
> By the way, why is 0xFD?

There is no reason. I just filled the page with unique number.

Thanks,
Yasuaki Ishimatsu

>
>>> + }
>>> + }
>>> +
>>> + free_pte_table(pmd);
>>> + __flush_tlb_all();
>>> +}
>>> +
>>> +static void vmemmap_pmd_remove(pud_t *pud, unsigned long addr, unsigned long end)
>>> +{
>>> + unsigned long next;
>>> + pmd_t *pmd;
>>> +
>>> + pmd = pmd_offset(pud, addr);
>>> + for (; addr < end; addr = next, pmd++) {
>>> + next = pmd_addr_end(addr, end);
>>> + if (pmd_none(*pmd))
>>> + continue;
>>> +
>>> + if (cpu_has_pse) {
>>> + unsigned long pte_base;
>>> +
>>> + if (IS_ALIGNED(addr, PMD_SIZE) &&
>>> + IS_ALIGNED(next, PMD_SIZE)) {
>>> + vmemmap_free_pages(pmd_page(*pmd),
>>> + get_order(PMD_SIZE));
>>> + 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 = get_zeroed_page(GFP_ATOMIC | __GFP_NOTRACK);
>>
>> get_zeored_page() may fail. You should handle this error.
>>
>
> That means system is out of memory, I will trigger a bug_on.
>
>>> + split_large_page((pte_t *)pmd, addr, (pte_t *)pte_base);
>>> + __flush_tlb_all();
>>> +
>>> + spin_lock(&init_mm.page_table_lock);
>>> + pmd_populate_kernel(&init_mm, pmd, (pte_t *)pte_base);
>>> + spin_unlock(&init_mm.page_table_lock);
>>> + }
>>> +
>>> + vmemmap_pte_remove(pmd, addr, next);
>>> + }
>>> +
>>> + free_pmd_table(pud);
>>> + __flush_tlb_all();
>>> +}
>>> +
>>> +static void vmemmap_pud_remove(pgd_t *pgd, unsigned long addr, unsigned long end)
>>> +{
>>> + unsigned long next;
>>> + pud_t *pud;
>>> +
>>> + pud = pud_offset(pgd, addr);
>>> + for (; addr < end; addr = next, pud++) {
>>> + next = pud_addr_end(addr, end);
>>> + if (pud_none(*pud))
>>> + continue;
>>> +
>>> + vmemmap_pmd_remove(pud, addr, next);
>>> + }
>>> +
>>> + free_pud_table(pgd);
>>> + __flush_tlb_all();
>>> +}
>>> +
>>> +void vmemmap_free(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> + unsigned long addr = (unsigned long)memmap;
>>> + unsigned long end = (unsigned long)(memmap + nr_pages);
>>> + unsigned long next;
>>> +
>>> + for (; addr < end; addr = next) {
>>> + pgd_t *pgd = pgd_offset_k(addr);
>>> +
>>> + next = pgd_addr_end(addr, end);
>>> + if (!pgd_present(*pgd))
>>> + continue;
>>> +
>>> + vmemmap_pud_remove(pgd, addr, next);
>>> + sync_global_pgds(addr, next);
>>
>> The parameter for sync_global_pgds() is [start, end], not
>> [start, end)
>>
>
> yes, thanks.
>
>>> + }
>>> +}
>>> +#endif
>>> diff --git a/mm/sparse.c b/mm/sparse.c
>>> index fac95f2..3a16d68 100644
>>> --- a/mm/sparse.c
>>> +++ b/mm/sparse.c
>>> @@ -613,12 +613,13 @@ static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid,
>>> /* This will make the necessary allocations eventually. */
>>> return sparse_mem_map_populate(pnum, nid);
>>> }
>>> -static void __kfree_section_memmap(struct page *memmap, unsigned long nr_pages)
>>> +static void __kfree_section_memmap(struct page *page, unsigned long nr_pages)
>> Why do you change this line?
>>
>
> 0k, it is no need to change.
>
>>> {
>>> - return; /* XXX: Not implemented yet */
>>> + vmemmap_free(page, nr_pages);
>>> }
>>> static void free_map_bootmem(struct page *page, unsigned long nr_pages)
>>> {
>>> + vmemmap_free(page, nr_pages);
>>> }
>>> #else
>>> static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
>>
>>
>> .
>>
>
>
>