On Fri, Sep 22, 2017 at 12:05:42PM +0100, Dr. David Alan Gilbert wrote:
[...]
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 7e20097..5d938e3 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -182,6 +182,70 @@ void ramblock_recv_bitmap_clear(RAMBlock *rb, void
> > *host_addr)
> > clear_bit(ramblock_recv_bitmap_offset(host_addr, rb), rb->receivedmap);
> > }
> >
> > +#define RAMBLOCK_RECV_BITMAP_ENDING (0x0123456789abcdefULL)
> > +
> > +/*
> > + * Format: bitmap_size (8 bytes) + whole_bitmap (N bytes).
> > + *
> > + * Returns >0 if success with sent bytes, or <0 if error.
> > + */
> > +int64_t ramblock_recv_bitmap_send(QEMUFile *file,
> > + const char *block_name)
> > +{
> > + RAMBlock *block = qemu_ram_block_by_name(block_name);
> > + unsigned long *le_bitmap, nbits;
> > + uint64_t size;
> > +
> > + if (!block) {
> > + error_report("%s: invalid block name: %s", __func__, block_name);
> > + return -1;
> > + }
> > +
> > + nbits = block->used_length >> TARGET_PAGE_BITS;
> > +
> > + /*
> > + * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit
> > + * machines we may need 4 more bytes for padding (see below
> > + * comment). So extend it a bit before hand.
> > + */
> > + le_bitmap = bitmap_new(nbits + BITS_PER_LONG);
>
> I do worry what will happen on really huge RAMBlocks; the worst case is
> that this temporary bitmap is a few GB.
IIUC the bitmap ratio is 32K, so the ramblock will be 1GB only if the
guest RAM region size is 1GB * 32K = 32TB.
Then, can I just assume allocating (only) 1GB temporary memory for a
guest using more than 32TB memory not a problem? :-)
I hope I didn't calculate it wrongly though.
>
> > + /*
> > + * Always use little endian when sending the bitmap. This is
> > + * required that when source and destination VMs are not using the
> > + * same endianess. (Note: big endian won't work.)
> > + */
> > + bitmap_to_le(le_bitmap, block->receivedmap, nbits);
> > +
> > + /* Size of the bitmap, in bytes */
> > + size = nbits / 8;
> > +
> > + /*
> > + * size is always aligned to 8 bytes for 64bit machines, but it
> > + * may not be true for 32bit machines. We need this padding to
> > + * make sure the migration can survive even between 32bit and
> > + * 64bit machines.
> > + */
> > + size = ROUND_UP(size, 8);
> > +
> > + qemu_put_be64(file, size);
> > + qemu_put_buffer(file, (const uint8_t *)le_bitmap, size);
> > + /*
> > + * Mark as an end, in case the middle part is screwed up due to
> > + * some "misterious" reason.
> > + */
> > + qemu_put_be64(file, RAMBLOCK_RECV_BITMAP_ENDING);
> > + qemu_fflush(file);
> > +
> > + free(le_bitmap);
> > +
> > + if (qemu_file_get_error(file)) {
> > + return qemu_file_get_error(file);
> > + }
> > +
> > + return size + sizeof(size);
> > +}
> > +
> > /*
> > * An outstanding page request, on the source, having been received
> > * and queued
> > @@ -2706,6 +2770,83 @@ static int ram_load(QEMUFile *f, void *opaque, int
> > version_id)
> > return ret;
> > }
> >
> > +/*
> > + * Read the received bitmap, revert it as the initial dirty bitmap.
> > + * This is only used when the postcopy migration is paused but wants
> > + * to resume from a middle point.
> > + */
> > +int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
> > +{
> > + int ret = -EINVAL;
> > + QEMUFile *file = s->rp_state.from_dst_file;
> > + unsigned long *le_bitmap, nbits = block->used_length >>
> > TARGET_PAGE_BITS;
> > + uint64_t local_size = nbits / 8;
> > + uint64_t size, end_mark;
> > +
> > + if (s->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
> > + error_report("%s: incorrect state %s", __func__,
> > + MigrationStatus_lookup[s->state]);
> > + return -EINVAL;
> > + }
> > +
> > + /*
> > + * Note: see comments in ramblock_recv_bitmap_send() on why we
> > + * need the endianess convertion, and the paddings.
> > + */
> > + local_size = ROUND_UP(local_size, 8);
> > +
> > + /* Add addings */
> > + le_bitmap = bitmap_new(nbits + BITS_PER_LONG);
> > +
> > + size = qemu_get_be64(file);
> > +
> > + /* The size of the bitmap should match with our ramblock */
> > + if (size != local_size) {
> > + error_report("%s: ramblock '%s' bitmap size mismatch "
> > + "(0x%lx != 0x%lx)", __func__, block->idstr,
> > + size, local_size);
>
> You need to use PRIx64 formatters there - %lx isn't portable.
Yes. Fixing.
>
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > +
> > + size = qemu_get_buffer(file, (uint8_t *)le_bitmap, local_size);
> > + end_mark = qemu_get_be64(file);
> > +
> > + ret = qemu_file_get_error(file);
> > + if (ret || size != local_size) {
> > + error_report("%s: read bitmap failed for ramblock '%s': %d",
> > + __func__, block->idstr, ret);
>
> You might like to include size/local_size in the error.
Will do. Thanks,
--
Peter Xu
