Re: [PATCH 1/5] migration: Rework migrate_send_rp_req_pages() function

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

* Peter Xu (peterx@redhat.com) wrote:
> We duplicated the logic of maintaining the last_rb variable at both callers of
> this function.  Pass *rb pointer into the function so that we can avoid
> duplicating the logic.  Also, when we have the rb pointer, it's also easier to
> remove the original 2nd & 4th parameters, because both of them (name of the
> ramblock when needed, or the page size) can be fetched from the ramblock
> pointer too.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

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

> ---
>  migration/migration.c    | 26 ++++++++++++++++++--------
>  migration/migration.h    |  4 ++--
>  migration/postcopy-ram.c | 24 ++----------------------
>  3 files changed, 22 insertions(+), 32 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 58a5452471..6761e3f233 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -311,25 +311,35 @@ error:
>      return ret;
>  }
>  
> -/* Request a range of pages from the source VM at the given
> - * start address.
> - *   rbname: Name of the RAMBlock to request the page in, if NULL it's the same
> - *           as the last request (a name must have been given previously)
> +/* Request one page from the source VM at the given start address.
> + *   rb: the RAMBlock to request the page in
>   *   Start: Address offset within the RB
>   *   Len: Length in bytes required - must be a multiple of pagesize
>   */
> -int migrate_send_rp_req_pages(MigrationIncomingState *mis, const char *rbname,
> -                              ram_addr_t start, size_t len)
> +int migrate_send_rp_req_pages(MigrationIncomingState *mis, RAMBlock *rb,
> +                              ram_addr_t start)
>  {
>      uint8_t bufc[12 + 1 + 255]; /* start (8), len (4), rbname up to 256 */
>      size_t msglen = 12; /* start + len */
> +    size_t len = qemu_ram_pagesize(rb);
>      enum mig_rp_message_type msg_type;
> +    const char *rbname;
> +    int rbname_len;
>  
>      *(uint64_t *)bufc = cpu_to_be64((uint64_t)start);
>      *(uint32_t *)(bufc + 8) = cpu_to_be32((uint32_t)len);
>  
> -    if (rbname) {
> -        int rbname_len = strlen(rbname);
> +    /*
> +     * We maintain the last ramblock that we requested for page.  Note that we
> +     * don't need locking because this function will only be called within the
> +     * postcopy ram fault thread.
> +     */
> +    if (rb != mis->last_rb) {
> +        mis->last_rb = rb;
> +
> +        rbname = qemu_ram_get_idstr(rb);
> +        rbname_len = strlen(rbname);
> +
>          assert(rbname_len < 256);
>  
>          bufc[msglen++] = rbname_len;
> diff --git a/migration/migration.h b/migration/migration.h
> index ae497bd45a..ca8dc4c773 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -328,8 +328,8 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
>                            uint32_t value);
>  void migrate_send_rp_pong(MigrationIncomingState *mis,
>                            uint32_t value);
> -int migrate_send_rp_req_pages(MigrationIncomingState *mis, const char* rbname,
> -                              ram_addr_t start, size_t len);
> +int migrate_send_rp_req_pages(MigrationIncomingState *mis, RAMBlock *rb,
> +                              ram_addr_t start);
>  void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
>                                   char *block_name);
>  void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value);
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 1bb22f2b6c..11a70441a6 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -684,14 +684,7 @@ int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
>                                          qemu_ram_get_idstr(rb), rb_offset);
>          return postcopy_wake_shared(pcfd, client_addr, rb);
>      }
> -    if (rb != mis->last_rb) {
> -        mis->last_rb = rb;
> -        migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
> -                                  aligned_rbo, pagesize);
> -    } else {
> -        /* Save some space */
> -        migrate_send_rp_req_pages(mis, NULL, aligned_rbo, pagesize);
> -    }
> +    migrate_send_rp_req_pages(mis, rb, aligned_rbo);
>      return 0;
>  }
>  
> @@ -986,20 +979,7 @@ retry:
>               * Send the request to the source - we want to request one
>               * of our host page sizes (which is >= TPS)
>               */
> -            if (rb != mis->last_rb) {
> -                mis->last_rb = rb;
> -                ret = migrate_send_rp_req_pages(mis,
> -                                                qemu_ram_get_idstr(rb),
> -                                                rb_offset,
> -                                                qemu_ram_pagesize(rb));
> -            } else {
> -                /* Save some space */
> -                ret = migrate_send_rp_req_pages(mis,
> -                                                NULL,
> -                                                rb_offset,
> -                                                qemu_ram_pagesize(rb));
> -            }
> -
> +            ret = migrate_send_rp_req_pages(mis, rb, rb_offset);
>              if (ret) {
>                  /* May be network failure, try to wait for recovery */
>                  if (ret == -EIO && postcopy_pause_fault_thread(mis)) {
> -- 
> 2.26.2
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK