Re: [PATCH v4 2/6] memory: make global_dirty_log a bitmask

[Hyman Huang <huangy81@chinatelecom.cn>]

在 2021/6/16 23:22, Peter Xu 写道:
> On Wed, Jun 16, 2021 at 09:12:28AM +0800, huangy81@chinatelecom.cn wrote:
>> diff --git a/include/exec/memory.h b/include/exec/memory.h
>> index b114f54..e31eef2 100644
>> --- a/include/exec/memory.h
>> +++ b/include/exec/memory.h
>> @@ -55,7 +55,11 @@ static inline void fuzz_dma_read_cb(size_t addr,
>>   }
>>   #endif
>>   
>> -extern bool global_dirty_log;
>> +/* what is the purpose of current dirty log, migration or dirty rate ? */
> 
> Nitpick: I'll make it:
> 
>    /* Possible bits for global_dirty_log */
> 
>    /* Dirty tracking enabled because migration is running */
>    #define GLOBAL_DIRTY_MIGRATION  (1U << 0)
> 
>    /* Dirty tracking enabled because measuring dirty rate */
>    #define GLOBAL_DIRTY_DIRTY_RATE (1U << 1)
> 
>> +#define GLOBAL_DIRTY_MIGRATION  (1U << 0)
>> +#define GLOBAL_DIRTY_DIRTY_RATE (1U << 1)
>> +
>> +extern unsigned int global_dirty_log;
>>   
>>   typedef struct MemoryRegionOps MemoryRegionOps;
>>   
> 
> [...]
> 
>> @@ -39,7 +39,7 @@
>>   static unsigned memory_region_transaction_depth;
>>   static bool memory_region_update_pending;
>>   static bool ioeventfd_update_pending;
>> -bool global_dirty_log;
>> +unsigned int global_dirty_log;
> 
> I'm wondering whether it's a good chance to rename it to global_dirty_tracking,
> because "logging" has a hint on the method while it's not the only one now.
yeah, all references to global_dirty_log should be modified and can this 
be done in a single patch before this patchset?
> 
>>   
>>   static QTAILQ_HEAD(, MemoryListener) memory_listeners
>>       = QTAILQ_HEAD_INITIALIZER(memory_listeners);
>> @@ -2659,14 +2659,19 @@ void memory_global_after_dirty_log_sync(void)
>>   
>>   static VMChangeStateEntry *vmstate_change;
>>   
>> -void memory_global_dirty_log_start(void)
>> +void memory_global_dirty_log_start(unsigned int flags)
>>   {
>>       if (vmstate_change) {
>>           qemu_del_vm_change_state_handler(vmstate_change);
>>           vmstate_change = NULL;
>>       }
>>   
>> -    global_dirty_log = true;
>> +#define  GLOBAL_DIRTY_MASK  (0x3)
>> +    assert(flags && !(flags & (~GLOBAL_DIRTY_MASK)));
>> +    assert(global_dirty_log ^ flags);
> 
> Heh, this is probably my fault... I think what I wanted to suggest is actually:
> 
>         assert(!(global_dirty_log & flags));
this is more graceful if concerning about only one of the reason can 
start dirty tracking at once. I'll pick up it in the next version.
> 
> Then for stop() below...
> 
>> +    global_dirty_log |= flags;
>> +
>> +    trace_global_dirty_changed(global_dirty_log);
>>   
>>       MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
>>   
>> @@ -2676,9 +2681,12 @@ void memory_global_dirty_log_start(void)
>>       memory_region_transaction_commit();
>>   }
>>   
>> -static void memory_global_dirty_log_do_stop(void)
>> +static void memory_global_dirty_log_do_stop(unsigned int flags)
>>   {
>> -    global_dirty_log = false;
>> +    assert(flags && !(flags & (~GLOBAL_DIRTY_MASK)));
> 
> ... it should probably be:
> 
>         assert((global_dirty_log & flags) == flags);
> 
> Sorry about the confusion.
not at all, since i'm not figure out how this bitmask works clearly, 
thanks a lot for your guidance.
> 

-- 
Best regard

Hyman Huang(黄勇)