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    SubjectRe: [RFC PATCH v3 11/13] memory-hotplug : free memmap of sparse-vmemmap
    At 07/11/2012 01:52 PM, Yasuaki Ishimatsu Wrote:
    > 2012/07/11 14:06, Wen Congyang wrote:
    > Hi Wen,
    >
    >> At 07/09/2012 06:33 PM, Yasuaki Ishimatsu Wrote:
    >>> I don't think that all pages of virtual mapping in removed memory can be
    >>> freed, since page which type is MIX_SECTION_INFO is difficult to free.
    >>> So, the patch only frees page which type is SECTION_INFO at first.
    >>>
    >>> 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 | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++
    >>> include/linux/mm.h | 2 +
    >>> mm/memory_hotplug.c | 5 ++
    >>> mm/sparse.c | 5 +-
    >>> 4 files changed, 101 insertions(+), 2 deletions(-)
    >>>
    >>> Index: linux-3.5-rc4/include/linux/mm.h
    >>> ===================================================================
    >>> --- linux-3.5-rc4.orig/include/linux/mm.h 2012-07-03 14:22:18.530011567 +0900
    >>> +++ linux-3.5-rc4/include/linux/mm.h 2012-07-03 14:22:20.999983872 +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-rc4/mm/sparse.c
    >>> ===================================================================
    >>> --- linux-3.5-rc4.orig/mm/sparse.c 2012-07-03 14:21:45.071429805 +0900
    >>> +++ linux-3.5-rc4/mm/sparse.c 2012-07-03 14:22:21.000983767 +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);
    >>
    >> Hmm, I think you try to free the memory allocated in kmalloc_section_memmap().
    >
    > Yes.
    >
    >>
    >>> }
    >>> static void free_map_bootmem(struct page *page, unsigned long nr_pages)
    >>> {
    >>> + vmemmap_free_bootmem(page, nr_pages);
    >>> }
    >>
    >> Hmm, which function is the memory you try to free allocated in?
    >
    > The function try to free memory allocated from bootmem. The memory has
    > been registered by get_page_bootmem(). So we can free the memory by
    > put_page_bootmem().

    OK, I will read these codes, and check it.

    >
    >>
    >>> #else
    >>> static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
    >>> Index: linux-3.5-rc4/arch/x86/mm/init_64.c
    >>> ===================================================================
    >>> --- linux-3.5-rc4.orig/arch/x86/mm/init_64.c 2012-07-03 14:22:18.538011465 +0900
    >>> +++ linux-3.5-rc4/arch/x86/mm/init_64.c 2012-07-03 14:22:21.007983103 +0900
    >>> @@ -978,6 +978,97 @@ vmemmap_populate(struct page *start_page
    >>> return 0;
    >>> }
    >>>
    >>> +unsigned long find_and_clear_pte_page(unsigned long addr, unsigned long end,
    >>> + struct page **pp)
    >>> +{
    >>> + pgd_t *pgd;
    >>> + pud_t *pud;
    >>> + pmd_t *pmd;
    >>> + pte_t *pte;
    >>> + unsigned long next;
    >>> +
    >>> + *pp = NULL;
    >>> +
    >>> + pgd = pgd_offset_k(addr);
    >>> + if (pgd_none(*pgd))
    >>> + return (addr + PAGE_SIZE) & PAGE_MASK;
    >>
    >> Hmm, why not goto next pgd?
    >
    > Does it mean "return (addr + PGDIR_SIZE) & PGDIR_MASK"?
    >
    >>
    >>> +
    >>> + pud = pud_offset(pgd, addr);
    >>> + if (pud_none(*pud))
    >>> + return (addr + PAGE_SIZE) & PAGE_MASK;
    >>> +
    >>> + 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;
    >>> +
    >>> + *pp = pte_page(*pte);
    >>> + pte_clear(&init_mm, addr, pte);
    >>
    >> I think you should flush tlb here.
    >
    > Thanks, I'll update it.
    >
    >>
    >>> + } else {
    >>> + next = pmd_addr_end(addr, end);
    >>> +
    >>> + pmd = pmd_offset(pud, addr);
    >>> + if (pmd_none(*pmd))
    >>> + return next;
    >>> +
    >>> + *pp = pmd_page(*pmd);
    >>> + pmd_clear(pmd);
    >>> + }
    >>> +
    >>> + return next;
    >>> +}
    >>> +
    >>> +void __meminit
    >>> +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;
    >>> + unsigned int order;
    >>> + struct page *page;
    >>> +
    >>> + for (; addr < end; addr = next) {
    >>> + page = NULL;
    >>> + next = find_and_clear_pte_page(addr, end, &page);
    >>> + if (!page)
    >>> + continue;
    >>> +
    >>> + if (is_vmalloc_addr(page_address(page)))
    >>> + vfree(page_address(page));
    >>
    >> Hmm, the memory is allocated in vmemmap_alloc_block(), and the address
    >> can not be vmalloc address.
    >
    > Does it mean the if sentence is unnecessary?
    >
    >>
    >>> + else {
    >>> + order = next - addr;
    >>> + free_pages((unsigned long)page_address(page),
    >>> + get_order(order));
    >>
    >> OOPS. I think we cannot free pages here.
    >>
    >> sizeof(struct page) is less than PAGE_SIZE. We store more than one struct
    >> page in the same page. If you free it here while the other struct page
    >> is in use, it is very dangerous.
    >
    > The memory has page structures for hot-removed memory. So nobody is using
    > these pages, since the hot-removed memory has been offlined.

    The memory has page structures for hot-removed memory, but it may contain
    page structures for the other hot-added memory.

    IIUC, If we use sparse-vmemmap, all page structures is stored here.

    Thanks
    Wen Congyang

    >
    >>> + }
    >>> + }
    >>> +}
    >>> +
    >>> +void __meminit
    >>> +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;
    >>> + unsigned long magic;
    >>> +
    >>> + for (; addr < end; addr = next) {
    >>> + page = NULL;
    >>> + next = find_and_clear_pte_page(addr, end, &page);
    >>> + if (!page)
    >>> + continue;
    >>> +
    >>> + magic = (unsigned long) page->lru.next;
    >>> + if (magic == SECTION_INFO)
    >>> + put_page_bootmem(page);
    >>> + }
    >>> +}
    >>> +
    >>> void __meminit
    >>> register_page_bootmem_memmap(unsigned long section_nr, struct page *start_page,
    >>> unsigned long size)
    >>> Index: linux-3.5-rc4/mm/memory_hotplug.c
    >>> ===================================================================
    >>> --- linux-3.5-rc4.orig/mm/memory_hotplug.c 2012-07-03 14:22:18.522011667 +0900
    >>> +++ linux-3.5-rc4/mm/memory_hotplug.c 2012-07-03 14:22:21.012982694 +0900
    >>> @@ -303,6 +303,8 @@ static int __meminit __add_section(int n
    >>> #ifdef CONFIG_SPARSEMEM_VMEMMAP
    >>
    >> I think this line can be removed now.
    >
    > I'll update it.
    >
    > Thanks,
    > Yasuaki Ishimatsu
    >
    >>
    >> Thanks
    >> Wen Congyang
    >>
    >>> static int __remove_section(struct zone *zone, struct mem_section *ms)
    >>> {
    >>> + unsigned long flags;
    >>> + struct pglist_data *pgdat = zone->zone_pgdat;
    >>> int ret;
    >>>
    >>> if (!valid_section(ms))
    >>> @@ -310,6 +312,9 @@ static int __remove_section(struct zone
    >>>
    >>> ret = unregister_memory_section(ms);
    >>>
    >>> + pgdat_resize_lock(pgdat, &flags);
    >>> + sparse_remove_one_section(zone, ms);
    >>> + pgdat_resize_unlock(pgdat, &flags);
    >>> return ret;
    >>> }
    >>> #else
    >>>
    >>>
    >>
    >
    >
    >
    >



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