Re: [PATCH v3 6/7] memory: make global_dirty_log a bitmask

[Peter Xu]

On Mon, Jun 07, 2021 at 09:13:12AM +0800, huangy81@chinatelecom.cn wrote:
> From: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
> 
> dirty rate measurement may start or stop dirty logging during
> calculation. this conflict with migration because stop dirty
> log make migration leave dirty pages out then that'll be a problem.
> 
> make global_dirty_log a bitmask can let both migration and dirty
> rate measurement work fine. introduce GLOBAL_DIRTY_MIGRATION and
> GLOBAL_DIRTY_DIRTY_RATE to distinguish what current dirty log aims
> for, migration or dirty rate.
> 
> all references to global_dirty_log should be untouched because any bit
> set there should justify that global dirty logging is enabled.
> 
> Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
> ---
>  include/exec/memory.h | 13 ++++++++++---
>  migration/ram.c       |  8 ++++----
>  softmmu/memory.c      | 36 +++++++++++++++++++++++++++---------
>  3 files changed, 41 insertions(+), 16 deletions(-)
> 
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index c158fd7084..94c7088299 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -55,7 +55,10 @@ static inline void fuzz_dma_read_cb(size_t addr,
>  }
>  #endif
>  
> -extern bool global_dirty_log;
> +#define GLOBAL_DIRTY_MIGRATION  (1U<<0)
> +#define GLOBAL_DIRTY_DIRTY_RATE (1U<<1)

Add some comment for each dirty log reason would be nice.

> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index c19b0be6b1..b93baba82d 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -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;
> +int global_dirty_log;

Maybe unsigned int would make more sense for a bitmask?

>  
>  static QTAILQ_HEAD(, MemoryListener) memory_listeners
>      = QTAILQ_HEAD_INITIALIZER(memory_listeners);
> @@ -2659,14 +2659,20 @@ 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(int flags)
>  {
>      if (vmstate_change) {
>          qemu_del_vm_change_state_handler(vmstate_change);
>          vmstate_change = NULL;
>      }
>  
> -    global_dirty_log = true;
> +    if (flags & GLOBAL_DIRTY_MIGRATION) {
> +        global_dirty_log |= GLOBAL_DIRTY_MIGRATION;
> +    }
> +
> +    if (flags & GLOBAL_DIRTY_DIRTY_RATE) {
> +        global_dirty_log |= GLOBAL_DIRTY_DIRTY_RATE;
> +    }

Instead of separate "if"s, perhaps something like this?

  #define  GLOBAL_DIRTY_MASK  (0x3)

  assert(!(flags & (~GLOBAL_DIRTY_MASK)));
  assert(!(global_dirty_log ^ flags));
  global_dirty_log |= flags;

>  
>      MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
>  
> @@ -2676,9 +2682,15 @@ 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(int flags)
>  {
> -    global_dirty_log = false;
> +    if (flags & GLOBAL_DIRTY_MIGRATION) {
> +        global_dirty_log &= ~GLOBAL_DIRTY_MIGRATION;
> +    }
> +
> +    if (flags & GLOBAL_DIRTY_DIRTY_RATE) {
> +        global_dirty_log &= ~GLOBAL_DIRTY_DIRTY_RATE;
> +    }

Same here?  Thanks,

-- 
Peter Xu