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

[Wei Yang <richardw.yang@linux.intel.com>]

On Tue, May 14, 2019 at 03:21:08PM +0100, Dr. David Alan Gilbert wrote:
>* 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?
>

Hi, Paolo,

Have time to take a look?

>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

-- 
Wei Yang
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