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

Jianguo Wu
2012-12-07T02:20:16Z

Hi Tang,

On 2012/12/7 9:42, Tang Chen wrote:

> Hi Wu,
>
> I met some problems when I was digging into the code. It's very
> kind of you if you could help me with that. :)
>
> If I misunderstood your code, please tell me.
> Please see below. :)
>
> On 12/03/2012 10:23 AM, Jianguo Wu wrote:
>> 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 | 231 +++++++++++++++++++++++++++++++++++++++++++++++++++
>> mm/sparse.c | 3 +-
>> 3 files changed, 234 insertions(+), 1 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..748732d 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 +228,230 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
>> vmemmap_buf_end = NULL;
>> }
>> }
>> +
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +
>> +#define PAGE_INUSE 0xFD
>> +
>> +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
>> + free_pages((unsigned long)page_address(page), order);
>
> Here, I think SECTION_INFO and MIX_SECTION_INFO pages are all allocated
> by bootmem, so I put this function this way.
>
> I'm not sure if parameter order is necessary here. It will always be 0
> in your code. Is this OK to you ?
>

parameter order is necessary in cpu_has_pse case:
vmemmap_pmd_remove
free_pagetable(pmd_page(*pmd), get_order(PMD_SIZE))

> static void free_pagetable(struct page *page)
> {
> struct zone *zone;
> bool bootmem = false;
> unsigned long magic;
>
> /* 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)
> put_page_bootmem(page);
> else
> __free_page(page);
>
> /*
> * 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++;
> zone_span_writeunlock(zone);
> totalram_pages++;
> }
> }
>
> (snip)
>
>> +
>> +static void vmemmap_pte_remove(pmd_t *pmd, unsigned long addr, unsigned long end)
>> +{
>> + pte_t *pte;
>> + unsigned long next;
>> + void *page_addr;
>> +
>> + 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))
>
> Here, you checked xxx_none() in your vmemmap_xxx_remove(), but you used
> !xxx_present() in your x86_64 patches. Is it OK if I only check
> !xxx_present() ?

It is Ok.

>
>> + continue;
>> + if (IS_ALIGNED(addr, PAGE_SIZE)&&
>> + IS_ALIGNED(next, 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);
>> + } else {
>> + /*
>> + * Removed page structs are 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)) {
>> + spin_lock(&init_mm.page_table_lock);
>> + pte_clear(&init_mm, addr, pte);
>> + spin_unlock(&init_mm.page_table_lock);
>
> Here, since we clear pte, we should also free the page, right ?
>

Right, I forgot here, sorry.

>> + }
>> + }
>> + }
>> +
>> + 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 = (addr, end);
>
> And by the way, there isn't pte_addr_end() in kernel, why ?
> I saw you calculated it like this:
>
> next = (addr + PAGE_SIZE) & PAGE_MASK;
> if (next > end)
> next = end;
>
> This logic is very similar to {pmd|pud|pgd}_addr_end(). Shall we add a
> pte_addr_end() or something ? :)

Maybe just keep this for now if no other place need pte_addr_end()?

> Since there is no such code in kernel for a long time, I think there
> must be some reasons.

Maybe in current kernel, doesn't deal not PTE_SIZE alignment addressï¼Ÿ

>
> I merged free_xxx_table() and remove_xxx_table() as common interfaces.

Greate!

Thanks for your work:).

>
> And again, thanks for your patient and nice explanation. :)
>
> (snip)
>
> .
>