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    SubjectRe: [RFC PATCH v4 11/13] memory-hotplug : free memmap of sparse-vmemmap
    At 07/18/2012 06:16 PM, Yasuaki Ishimatsu Wrote:
    > All pages of virtual mapping in removed memory cannot be freed, since some pages
    > used as PGD/PUD includes not only removed memory but also other memory. So the
    > patch checks whether page can be freed or not.
    >
    > How 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.
    >
    > Applying patch, __remove_section() of CONFIG_SPARSEMEM_VMEMMAP is integrated
    > into one. So __remove_section() of CONFIG_SPARSEMEM_VMEMMAP is deleted.
    >
    > CC: David Rientjes <rientjes@google.com>
    > CC: Jiang Liu <liuj97@gmail.com>
    > CC: Len Brown <len.brown@intel.com>
    > CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    > CC: Paul Mackerras <paulus@samba.org>
    > CC: Christoph Lameter <cl@linux.com>
    > Cc: Minchan Kim <minchan.kim@gmail.com>
    > CC: Andrew Morton <akpm@linux-foundation.org>
    > CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > CC: Wen Congyang <wency@cn.fujitsu.com>
    > Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    >
    > ---
    > arch/x86/mm/init_64.c | 121 ++++++++++++++++++++++++++++++++++++++++++++++++++
    > include/linux/mm.h | 2
    > mm/memory_hotplug.c | 19 -------
    > mm/sparse.c | 5 +-
    > 4 files changed, 128 insertions(+), 19 deletions(-)
    >
    > Index: linux-3.5-rc6/include/linux/mm.h
    > ===================================================================
    > --- linux-3.5-rc6.orig/include/linux/mm.h 2012-07-18 18:01:28.000000000 +0900
    > +++ linux-3.5-rc6/include/linux/mm.h 2012-07-18 18:03:05.551168773 +0900
    > @@ -1588,6 +1588,8 @@ int vmemmap_populate(struct page *start_
    > void vmemmap_populate_print_last(void);
    > void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
    > unsigned long size);
    > +void vmemmap_kfree(struct page *memmpa, unsigned long nr_pages);
    > +void vmemmap_free_bootmem(struct page *memmpa, unsigned long nr_pages);
    >
    > enum mf_flags {
    > MF_COUNT_INCREASED = 1 << 0,
    > Index: linux-3.5-rc6/mm/sparse.c
    > ===================================================================
    > --- linux-3.5-rc6.orig/mm/sparse.c 2012-07-18 17:59:25.000000000 +0900
    > +++ linux-3.5-rc6/mm/sparse.c 2012-07-18 18:03:05.553168749 +0900
    > @@ -614,12 +614,13 @@ static inline struct page *kmalloc_secti
    > /* 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)
    > {
    > - return; /* XXX: Not implemented yet */
    > + vmemmap_kfree(page, nr_pages);
    > }
    > static void free_map_bootmem(struct page *page, unsigned long nr_pages)
    > {
    > + vmemmap_free_bootmem(page, nr_pages);
    > }
    > #else
    > static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
    > Index: linux-3.5-rc6/arch/x86/mm/init_64.c
    > ===================================================================
    > --- linux-3.5-rc6.orig/arch/x86/mm/init_64.c 2012-07-18 18:01:28.000000000 +0900
    > +++ linux-3.5-rc6/arch/x86/mm/init_64.c 2012-07-18 18:03:05.564168611 +0900
    > @@ -978,6 +978,127 @@ vmemmap_populate(struct page *start_page
    > return 0;
    > }
    >
    > +#define PAGE_INUSE 0xFD
    > +
    > +unsigned long find_and_clear_pte_page(unsigned long addr, unsigned long end,
    > + struct page **pp, int *page_size)
    > +{
    > + pgd_t *pgd;
    > + pud_t *pud;
    > + pmd_t *pmd;
    > + pte_t *pte;
    > + void *page_addr;
    > + unsigned long next;
    > +
    > + *pp = NULL;
    > +
    > + pgd = pgd_offset_k(addr);
    > + if (pgd_none(*pgd))
    > + return pgd_addr_end(addr, end);
    > +
    > + pud = pud_offset(pgd, addr);
    > + if (pud_none(*pud))
    > + return pud_addr_end(addr,end);
    > +
    > + if (!cpu_has_pse) {
    > + next = (addr + PAGE_SIZE) & PAGE_MASK;
    > + pmd = pmd_offset(pud, addr);
    > + if (pmd_none(*pmd))
    > + return next;
    > +
    > + pte = pte_offset_kernel(pmd, addr);
    > + if (pte_none(*pte))
    > + return next;
    > +
    > + *page_size = PAGE_SIZE;
    > + *pp = pte_page(*pte);
    > + } else {
    > + next = pmd_addr_end(addr, end);
    > +
    > + pmd = pmd_offset(pud, addr);
    > + if (pmd_none(*pmd))
    > + return next;
    > +
    > + *page_size = PMD_SIZE;
    > + *pp = pmd_page(*pmd);
    > + }
    > +
    > + /*
    > + * Removed page structs are filled with 0xFD.
    > + */
    > + memset((void *)addr, PAGE_INUSE, next - addr);
    > +
    > + page_addr = page_address(*pp);
    > +
    > + /*
    > + * Check the page is filled with 0xFD or not.
    > + * memchr_inv() returns the address. In this case, we cannot
    > + * clear PTE/PUD entry, since the page is used by other.
    > + * So we cannot also free the page.
    > + *
    > + * memchr_inv() returns NULL. In this case, we can clear
    > + * PTE/PUD entry, since the page is not used by other.
    > + * So we can also free the page.
    > + */
    > + if (memchr_inv(page_addr, PAGE_INUSE, *page_size)) {
    > + *pp = NULL;
    > + return next;
    > + }
    > +
    > + if (!cpu_has_pse)
    > + pte_clear(&init_mm, addr, pte);
    > + else
    > + pmd_clear(pmd);
    > +
    > + return next;
    > +}
    > +
    > +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
    > +{
    > + unsigned long addr = (unsigned long)memmap;
    > + unsigned long end = (unsigned long)(memmap + nr_pages);
    > + unsigned long next;
    > + struct page *page;
    > + int page_size;
    > +
    > + for (; addr < end; addr = next) {
    > + page = NULL;
    > + page_size = 0;
    > + next = find_and_clear_pte_page(addr, end, &page, &page_size);
    > + if (!page)
    > + continue;
    > +
    > + free_pages((unsigned long)page_address(page),
    > + get_order(page_size));
    > + __flush_tlb_one((unsigned long)page_address(page));
    > + }
    > +
    > +}
    > +
    > +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
    > +{
    > + unsigned long addr = (unsigned long)memmap;
    > + unsigned long end = (unsigned long)(memmap + nr_pages);
    > + unsigned long next;
    > + struct page *page;
    > + int page_size;
    > + unsigned long magic;
    > +
    > + for (; addr < end; addr = next) {
    > + page = NULL;
    > + page_size = 0;
    > + next = find_and_clear_pte_page(addr, end, &page, &page_size);
    > + if (!page)
    > + continue;
    > +
    > + magic = (unsigned long) page->lru.next;
    > + if (magic == SECTION_INFO)
    > + put_page_bootmem(page);
    > + flush_tlb_kernel_range(addr, end);
    > + }
    > +
    > +}
    > +
    > void register_page_bootmem_memmap(unsigned long section_nr,
    > struct page *start_page, unsigned long size)
    > {
    > Index: linux-3.5-rc6/mm/memory_hotplug.c
    > ===================================================================
    > --- linux-3.5-rc6.orig/mm/memory_hotplug.c 2012-07-18 18:01:28.000000000 +0900
    > +++ linux-3.5-rc6/mm/memory_hotplug.c 2012-07-18 18:25:11.036597977 +0900
    > @@ -300,7 +300,6 @@ static int __meminit __add_section(int n
    > return register_new_memory(nid, __pfn_to_section(phys_start_pfn));
    > }
    >
    > -#ifdef CONFIG_SPARSEMEM_VMEMMAP
    > static int __remove_section(struct zone *zone, struct mem_section *ms)
    > {
    > int ret = -EINVAL;
    > @@ -309,29 +308,15 @@ static int __remove_section(struct zone
    > return ret;
    >
    > ret = unregister_memory_section(ms);
    > -
    > - return ret;
    > -}
    > -#else
    > -static int __remove_section(struct zone *zone, struct mem_section *ms)
    > -{
    > - unsigned long flags;
    > - struct pglist_data *pgdat = zone->zone_pgdat;

    This two line should not be removed. Otherwise, we can not build the kernel.

    Thanks
    Wen Congyang

    > - int ret = -EINVAL;
    > -
    > - if (!valid_section(ms))
    > - return ret;
    > -
    > - ret = unregister_memory_section(ms);
    > if (ret)
    > return ret;
    >
    > pgdat_resize_lock(pgdat, &flags);
    > sparse_remove_one_section(zone, ms);
    > pgdat_resize_unlock(pgdat, &flags);
    > - return 0;
    > +
    > + return ret;
    > }
    > -#endif
    >
    > /*
    > * Reasonably generic function for adding memory. It is
    >
    > --
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