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

Tang Chen <tangchen@xxxxxxxxxxxxxx> · Fri, 07 Dec 2012 09:42:14 +0800

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@xxxxxxxxxx>
Signed-off-by: Jiang Liu<jiang.liu@xxxxxxxxxx>
---
  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)
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