Re: [Qemu-devel] [PATCH 2/2] migration: discard non-dirty ram pages after the start of postcopy

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

* Pavel Butsykin (pbutsykin@virtuozzo.com) wrote:
> After the start of postcopy migration there are some non-dirty pages which have
> already been migrated. These pages are no longer needed on the source vm so that
> we can free them and it doen't hurt to complete the migration.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  include/migration/migration.h |  1 +
>  migration/migration.c         |  2 ++
>  migration/ram.c               | 25 +++++++++++++++++++++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index d7bd404365..0d9b81545c 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -279,6 +279,7 @@ int ram_postcopy_send_discard_bitmap(MigrationState *ms);
>  int ram_discard_range(MigrationIncomingState *mis, const char *block_name,
>                        uint64_t start, size_t length);
>  int ram_postcopy_incoming_init(MigrationIncomingState *mis);
> +void ram_postcopy_migrated_memory_discard(MigrationState *ms);
>  
>  /**
>   * @migrate_add_blocker - prevent migration from proceeding
> diff --git a/migration/migration.c b/migration/migration.c
> index 391db6f28b..20490ed020 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1662,6 +1662,8 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
>       */
>      qemu_savevm_send_ping(ms->to_dst_file, 4);
>  
> +    ram_postcopy_migrated_memory_discard(ms);
> +

Did you intend this to be selected based on your capability flag?


>      ret = qemu_file_get_error(ms->to_dst_file);
>      if (ret) {
>          error_report("postcopy_start: Migration stream errored");
> diff --git a/migration/ram.c b/migration/ram.c
> index b0322a0b5c..8a6b614b0d 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1546,6 +1546,31 @@ void ram_debug_dump_bitmap(unsigned long *todump, bool expected)
>  
>  /* **** functions for postcopy ***** */
>  
> +void ram_postcopy_migrated_memory_discard(MigrationState *ms)
> +{
> +    struct RAMBlock *block;
> +    unsigned long *bitmap = atomic_rcu_read(&migration_bitmap_rcu)->bmap;
> +
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        unsigned long first = block->offset >> TARGET_PAGE_BITS;
> +        unsigned long range = first + (block->used_length >> TARGET_PAGE_BITS);
> +        unsigned long run_start = find_next_zero_bit(bitmap, range, first);
> +
> +        while (run_start < range) {
> +            unsigned long run_end = find_next_bit(bitmap, range, run_start + 1);
> +            uint8_t *addr = block->host + (run_start << TARGET_PAGE_BITS);
> +            size_t chunk_size = (run_end - run_start) << TARGET_PAGE_BITS;
> +
> +            if (qemu_madvise(addr, chunk_size, QEMU_MADV_DONTNEED) < 0) {
> +                error_report("migrate: madvise DONTNEED failed %p %ld: %s",
> +                             addr, chunk_size, strerror(errno));
> +            }

can you use your ram_discard_page here, it keeps all the use of madvise together.
> +
> +            run_start = find_next_zero_bit(bitmap, range, run_end + 1);
> +        }
> +    }
> +}

Dave

>  /*
>   * Callback from postcopy_each_ram_send_discard for each RAMBlock
>   * Note: At this point the 'unsentmap' is the processed bitmap combined
> -- 
> 2.11.0
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK