Re: [RFC PATCH v2 3/3] Per memslot dirty bitmap

Marcelo Tosatti
2011-08-02T16:29:22Z

On Fri, Jul 29, 2011 at 04:57:26PM -0400, Umesh Deshpande wrote:
> This patch creates a separate dirty bitmap for each slot. Currently dirty bitmap
> is created for addresses ranging from 0 to the end address of the last memory
> slot. Since the memslots are not necessarily contiguous, current bitmap might
> contain empty region or holes that doesn't represent any VM pages. This patch
> reduces the size of the dirty bitmap by allocating per memslot dirty bitmaps.
>
> Signed-off-by: Umesh Deshpande <udeshpan@redhat.com>
> ---
> cpu-all.h | 40 +++++++++++++++++++++++++++++++++-------
> exec.c | 38 +++++++++++++++++++++++---------------
> xen-all.c | 6 ++----
> 3 files changed, 58 insertions(+), 26 deletions(-)
>
> diff --git a/cpu-all.h b/cpu-all.h
> index e839100..9517a9b 100644
> --- a/cpu-all.h
> +++ b/cpu-all.h
> @@ -920,6 +920,7 @@ extern ram_addr_t ram_size;
>
> typedef struct RAMBlock {
> uint8_t *host;
> + uint8_t *phys_dirty;
> ram_addr_t offset;
> ram_addr_t length;
> uint32_t flags;
> @@ -931,7 +932,6 @@ typedef struct RAMBlock {
> } RAMBlock;
>
> typedef struct RAMList {
> - uint8_t *phys_dirty;
> QLIST_HEAD(ram, RAMBlock) blocks;
> } RAMList;
> extern RAMList ram_list;
> @@ -961,32 +961,55 @@ extern int mem_prealloc;
> #define CODE_DIRTY_FLAG 0x02
> #define MIGRATION_DIRTY_FLAG 0x08
>
> +RAMBlock *qemu_addr_to_ramblock(ram_addr_t);
> +
> +static inline int get_page_nr(ram_addr_t addr, RAMBlock **block)
> +{
> + int page_nr;
> + *block = qemu_addr_to_ramblock(addr);
> +
> + page_nr = addr - (*block)->offset;
> + page_nr = page_nr >> TARGET_PAGE_BITS;
> +
> + return page_nr;
> +}
> +
> /* read dirty bit (return 0 or 1) */
> static inline int cpu_physical_memory_is_dirty(ram_addr_t addr)
> {
> - return ram_list.phys_dirty[addr >> TARGET_PAGE_BITS] == 0xff;
> + RAMBlock *block;
> + int page_nr = get_page_nr(addr, &block);
> + return block->phys_dirty[page_nr] == 0xff;
> }
>
> static inline int cpu_physical_memory_get_dirty_flags(ram_addr_t addr)
> {
> - return ram_list.phys_dirty[addr >> TARGET_PAGE_BITS];
> + RAMBlock *block;
> + int page_nr = get_page_nr(addr, &block);
> + return block->phys_dirty[page_nr];
> }
>
> static inline int cpu_physical_memory_get_dirty(ram_addr_t addr,
> int dirty_flags)
> {
> - return ram_list.phys_dirty[addr >> TARGET_PAGE_BITS] & dirty_flags;
> + RAMBlock *block;
> + int page_nr = get_page_nr(addr, &block);
> + return block->phys_dirty[page_nr] & dirty_flags;
> }
>
> static inline void cpu_physical_memory_set_dirty(ram_addr_t addr)
> {
> - ram_list.phys_dirty[addr >> TARGET_PAGE_BITS] = 0xff;
> + RAMBlock *block;
> + int page_nr = get_page_nr(addr, &block);
> + block->phys_dirty[page_nr] = 0xff;
> }
>
> static inline int cpu_physical_memory_set_dirty_flags(ram_addr_t addr,
> int dirty_flags)
> {
> - return ram_list.phys_dirty[addr >> TARGET_PAGE_BITS] |= dirty_flags;
> + RAMBlock *block;
> + int page_nr = get_page_nr(addr, &block);
> + return block->phys_dirty[page_nr] |= dirty_flags;
> }
>
> static inline void cpu_physical_memory_mask_dirty_range(ram_addr_t start,
> @@ -995,10 +1018,13 @@ static inline void cpu_physical_memory_mask_dirty_range(ram_addr_t start,
> {
> int i, mask, len;
> uint8_t *p;
> + RAMBlock *block;
> + int page_nr = get_page_nr(start, &block);
>
> len = length >> TARGET_PAGE_BITS;
> mask = ~dirty_flags;
> - p = ram_list.phys_dirty + (start >> TARGET_PAGE_BITS);
> +
> + p = block->phys_dirty + page_nr;
> p[i] &= mask;
> }
> diff --git a/exec.c b/exec.c
> index 0e2ce57..6312550 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2106,6 +2106,10 @@ void cpu_physical_memory_reset_dirty(ram_addr_t start, ram_addr_t end,
> abort();
> }
>
> + if (kvm_enabled()) {
> + return;
> + }
> +

This belongs to a separate patch.