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

Tang Chen
2012-12-07T01:42:14Z

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 ?

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() ?

> + 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 ?

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

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

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

(snip)