Re: [Qemu-devel] [PATCH 2/3] migration/ram.c: start of cpu_physical_memory_sync_dirty_bitmap is always 0

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> Since start of cpu_physical_memory_sync_dirty_bitmap is always 0, we can
> remove this parameter and simplify the calculation a bit.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

So I think you're right it's currently unused; however, lets ask
Paolo: Do we need to keep this parameter for flexiblity?

Dave

> ---
>  include/exec/ram_addr.h | 15 ++++++---------
>  migration/ram.c         |  2 +-
>  2 files changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 9ecd911c3e..3dfb2d52fb 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -409,18 +409,16 @@ static inline void cpu_physical_memory_clear_dirty_range(ram_addr_t start,
>  
>  static inline
>  uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
> -                                               ram_addr_t start,
>                                                 ram_addr_t length,
>                                                 uint64_t *real_dirty_pages)
>  {
>      ram_addr_t addr;
> -    unsigned long word = BIT_WORD((start + rb->offset) >> TARGET_PAGE_BITS);
> +    unsigned long word = BIT_WORD(rb->offset >> TARGET_PAGE_BITS);
>      uint64_t num_dirty = 0;
>      unsigned long *dest = rb->bmap;
>  
> -    /* start address and length is aligned at the start of a word? */
> -    if (((word * BITS_PER_LONG) << TARGET_PAGE_BITS) ==
> -         (start + rb->offset) &&
> +    /* offset and length is aligned at the start of a word? */
> +    if (((word * BITS_PER_LONG) << TARGET_PAGE_BITS) == (rb->offset) &&
>          !(length & ((BITS_PER_LONG << TARGET_PAGE_BITS) - 1))) {
>          int k;
>          int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS);
> @@ -428,14 +426,13 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
>          unsigned long idx = (word * BITS_PER_LONG) / DIRTY_MEMORY_BLOCK_SIZE;
>          unsigned long offset = BIT_WORD((word * BITS_PER_LONG) %
>                                          DIRTY_MEMORY_BLOCK_SIZE);
> -        unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
>  
>          rcu_read_lock();
>  
>          src = atomic_rcu_read(
>                  &ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION])->blocks;
>  
> -        for (k = page; k < page + nr; k++) {
> +        for (k = 0; k < nr; k++) {
>              if (src[idx][offset]) {
>                  unsigned long bits = atomic_xchg(&src[idx][offset], 0);
>                  unsigned long new_dirty;
> @@ -458,11 +455,11 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
>  
>          for (addr = 0; addr < length; addr += TARGET_PAGE_SIZE) {
>              if (cpu_physical_memory_test_and_clear_dirty(
> -                        start + addr + offset,
> +                        addr + offset,
>                          TARGET_PAGE_SIZE,
>                          DIRTY_MEMORY_MIGRATION)) {
>                  *real_dirty_pages += 1;
> -                long k = (start + addr) >> TARGET_PAGE_BITS;
> +                long k = addr >> TARGET_PAGE_BITS;
>                  if (!test_and_set_bit(k, dest)) {
>                      num_dirty++;
>                  }
> diff --git a/migration/ram.c b/migration/ram.c
> index 9948b2d021..1def8122e9 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1646,7 +1646,7 @@ static void migration_bitmap_sync_range(RAMState *rs, RAMBlock *rb,
>                                          ram_addr_t length)
>  {
>      rs->migration_dirty_pages +=
> -        cpu_physical_memory_sync_dirty_bitmap(rb, 0, length,
> +        cpu_physical_memory_sync_dirty_bitmap(rb, length,
>                                                &rs->num_dirty_pages_period);
>  }
>  
> -- 
> 2.19.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK