Re: [Qemu-devel] [PATCH v5 17/29] vhost+postcopy: Helper to send requests to source for shared pages

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Mar 12, 2018 at 05:21:12PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Provide a helper to be used by shared waker functions to request
> shared pages from the source.
> The last_rb pointer is moved into the incoming state since this
> helper can update it as well as the main fault thread function.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  migration/migration.h    |  2 ++
>  migration/postcopy-ram.c | 32 +++++++++++++++++++++++++++++---
>  migration/postcopy-ram.h |  3 +++
>  migration/trace-events   |  2 ++
>  4 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/migration/migration.h b/migration/migration.h
> index d02a759331..83dc36b57a 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -49,6 +49,8 @@ struct MigrationIncomingState {
>      int       userfault_event_fd;
>      QEMUFile *to_src_file;
>      QemuMutex rp_mutex;    /* We send replies from multiple threads */
> +    /* RAMBlock of last request sent to source */
> +    RAMBlock *last_rb;
>      void     *postcopy_tmp_page;
>      void     *postcopy_tmp_zero_page;
>      /* PostCopyFD's for external userfaultfds & handlers of shared memory */
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 4ab1b7d36d..83780576ca 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -525,6 +525,32 @@ static int ram_block_enable_notify(const char *block_name, void *host_addr,
>      return 0;
>  }
>  
> +/*
> + * Callback from shared fault handlers to ask for a page,
> + * the page must be specified by a RAMBlock and an offset in that rb
> + * Note: Only for use by shared fault handlers (in fault thread)
> + */
> +int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
> +                                 uint64_t client_addr, uint64_t rb_offset)
> +{
> +    size_t pagesize = qemu_ram_pagesize(rb);
> +    uint64_t aligned_rbo = rb_offset & ~(pagesize - 1);
> +    MigrationIncomingState *mis = migration_incoming_get_current();
> +
> +    trace_postcopy_request_shared_page(pcfd->idstr, qemu_ram_get_idstr(rb),
> +                                       rb_offset);
> +    /* TODO: Check bitmap to see if we already have the page */
> +    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);
> +    }
> +    return 0;
> +}
> +
>  /*
>   * Handle faults detected by the USERFAULT markings
>   */
> @@ -535,9 +561,9 @@ static void *postcopy_ram_fault_thread(void *opaque)
>      int ret;
>      size_t index;
>      RAMBlock *rb = NULL;
> -    RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */
>  
>      trace_postcopy_ram_fault_thread_entry();
> +    mis->last_rb = NULL; /* last RAMBlock we sent part of */
>      qemu_sem_post(&mis->fault_thread_sem);
>  
>      struct pollfd *pfd;
> @@ -636,8 +662,8 @@ static void *postcopy_ram_fault_thread(void *opaque)
>               * Send the request to the source - we want to request one
>               * of our host page sizes (which is >= TPS)
>               */
> -            if (rb != last_rb) {
> -                last_rb = rb;
> +            if (rb != mis->last_rb) {
> +                mis->last_rb = rb;
>                  migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
>                                           rb_offset, qemu_ram_pagesize(rb));
>              } else {
> diff --git a/migration/postcopy-ram.h b/migration/postcopy-ram.h
> index c8ced3470b..d7afab07d7 100644
> --- a/migration/postcopy-ram.h
> +++ b/migration/postcopy-ram.h
> @@ -164,5 +164,8 @@ struct PostCopyFD {
>   */
>  void postcopy_register_shared_ufd(struct PostCopyFD *pcfd);
>  void postcopy_unregister_shared_ufd(struct PostCopyFD *pcfd);
> +/* Callback from shared fault handlers to ask for a page */
> +int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
> +                                 uint64_t client_addr, uint64_t offset);
>  
>  #endif
> diff --git a/migration/trace-events b/migration/trace-events
> index 1e617ad7a6..7c910b5479 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -198,6 +198,8 @@ postcopy_ram_incoming_cleanup_closeuf(void) ""
>  postcopy_ram_incoming_cleanup_entry(void) ""
>  postcopy_ram_incoming_cleanup_exit(void) ""
>  postcopy_ram_incoming_cleanup_join(void) ""
> +postcopy_request_shared_page(const char *sharer, const char *rb, uint64_t rb_offset) "for %s in %s offset 0x%"PRIx64
> +
>  save_xbzrle_page_skipping(void) ""
>  save_xbzrle_page_overflow(void) ""
>  ram_save_iterate_big_wait(uint64_t milliconds, int iterations) "big wait: %" PRIu64 " milliseconds, %d iterations"

So this function was missing a stub.

For the record, since 1842bdfdbac2ec46f2934d8914c874db83dd1344 we have
a copy of linux system headers so ifdef for NR_userfaultfd
is unnecessary on linux.

Let's just drop it?

> -- 
> 2.14.3