Re: [Qemu-devel] [PATCH v3 1/3] migration: API to clear bits of guest free pages from the dirty bitmap

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

* Wei Wang (wei.w.wang@intel.com) wrote:
> This patch adds an API to clear bits corresponding to guest free pages
> from the dirty bitmap. Spilt the free page block if it crosses the QEMU
> RAMBlock boundary.
> 
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  include/migration/misc.h |  2 ++
>  migration/ram.c          | 20 ++++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/include/migration/misc.h b/include/migration/misc.h
> index 77fd4f5..fae1acf 100644
> --- a/include/migration/misc.h
> +++ b/include/migration/misc.h
> @@ -14,11 +14,13 @@
>  #ifndef MIGRATION_MISC_H
>  #define MIGRATION_MISC_H
>  
> +#include "exec/cpu-common.h"
>  #include "qemu/notify.h"
>  
>  /* migration/ram.c */
>  
>  void ram_mig_init(void);
> +void qemu_guest_free_page_hint(void *addr, size_t len);
>  
>  /* migration/block.c */
>  
> diff --git a/migration/ram.c b/migration/ram.c
> index 5e33e5c..769a0f6 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2189,6 +2189,26 @@ static int ram_init_all(RAMState **rsp)
>      return 0;
>  }
>  
> +void qemu_guest_free_page_hint(void *addr, size_t len)
> +{
> +    RAMBlock *block;
> +    ram_addr_t offset;
> +    size_t used_len, start, npages;
> +
> +    for (used_len = len; len > 0; len -= used_len) {
> +        block = qemu_ram_block_from_host(addr, false, &offset);
> +        if (unlikely(offset + len > block->used_length)) {
> +            used_len = block->used_length - offset;
> +            addr += used_len;
> +        }
> +
> +        start = offset >> TARGET_PAGE_BITS;
> +        npages = used_len >> TARGET_PAGE_BITS;
> +        bitmap_clear(block->bmap, start, npages);
> +        ram_state->migration_dirty_pages -= npages;
> +    }
> +}
> +
>  /*
>   * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
>   * long-running RCU critical section.  When rcu-reclaims in the code
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK