Re: [Qemu-devel] [PATCH v2 2/3] add 'release-ram' migrate capability

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

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Pavel Butsykin (pbutsykin@virtuozzo.com) wrote:
> > This feature frees the migrated memory on the source during postcopy-ram
> > migration. In the second step of postcopy-ram migration when the source vm
> > is put on pause we can free unnecessary memory. It will allow, in particular,
> > to start relaxing the memory stress on the source host in a load-balancing
> > scenario.
> > 
> > Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Actually, note the error from patchew;  you need to fix up the error reports
that print iov_len to %zd I think.

Dave

> > ---
> >  include/migration/migration.h |  1 +
> >  include/migration/qemu-file.h |  3 ++-
> >  migration/migration.c         |  9 +++++++
> >  migration/qemu-file.c         | 59 ++++++++++++++++++++++++++++++++++++++-----
> >  migration/ram.c               | 22 +++++++++++++++-
> >  qapi-schema.json              |  5 +++-
> >  6 files changed, 89 insertions(+), 10 deletions(-)
> > 
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index bd399fc0df..401fbe1f77 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -307,6 +307,7 @@ int migrate_add_blocker(Error *reason, Error **errp);
> >   */
> >  void migrate_del_blocker(Error *reason);
> >  
> > +bool migrate_release_ram(void);
> >  bool migrate_postcopy_ram(void);
> >  bool migrate_zero_blocks(void);
> >  
> > diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
> > index abedd466c9..0cd648a733 100644
> > --- a/include/migration/qemu-file.h
> > +++ b/include/migration/qemu-file.h
> > @@ -132,7 +132,8 @@ void qemu_put_byte(QEMUFile *f, int v);
> >   * put_buffer without copying the buffer.
> >   * The buffer should be available till it is sent asynchronously.
> >   */
> > -void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size);
> > +void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
> > +                           bool may_free);
> >  bool qemu_file_mode_is_not_valid(const char *mode);
> >  bool qemu_file_is_writable(QEMUFile *f);
> >  
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 1ae68be0c7..8d5a5f8a6e 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1302,6 +1302,15 @@ void qmp_migrate_set_downtime(double value, Error **errp)
> >      qmp_migrate_set_parameters(&p, errp);
> >  }
> >  
> > +bool migrate_release_ram(void)
> > +{
> > +    MigrationState *s;
> > +
> > +    s = migrate_get_current();
> > +
> > +    return s->enabled_capabilities[MIGRATION_CAPABILITY_RELEASE_RAM];
> > +}
> > +
> >  bool migrate_postcopy_ram(void)
> >  {
> >      MigrationState *s;
> > diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> > index e9fae31158..82dbef3c86 100644
> > --- a/migration/qemu-file.c
> > +++ b/migration/qemu-file.c
> > @@ -49,6 +49,7 @@ struct QEMUFile {
> >      int buf_size; /* 0 when writing */
> >      uint8_t buf[IO_BUF_SIZE];
> >  
> > +    DECLARE_BITMAP(may_free, MAX_IOV_SIZE);
> >      struct iovec iov[MAX_IOV_SIZE];
> >      unsigned int iovcnt;
> >  
> > @@ -132,6 +133,41 @@ bool qemu_file_is_writable(QEMUFile *f)
> >      return f->ops->writev_buffer;
> >  }
> >  
> > +static void qemu_iovec_release_ram(QEMUFile *f)
> > +{
> > +    struct iovec iov;
> > +    unsigned long idx;
> > +
> > +    /* Find and release all the contiguous memory ranges marked as may_free. */
> > +    idx = find_next_bit(f->may_free, f->iovcnt, 0);
> > +    if (idx >= f->iovcnt) {
> > +        return;
> > +    }
> > +    iov = f->iov[idx];
> > +
> > +    /* The madvise() in the loop is called for iov within a continuous range and
> > +     * then reinitialize the iov. And in the end, madvise() is called for the
> > +     * last iov.
> > +     */
> > +    while ((idx = find_next_bit(f->may_free, f->iovcnt, idx + 1)) < f->iovcnt) {
> > +        /* check for adjacent buffer and coalesce them */
> > +        if (iov.iov_base + iov.iov_len == f->iov[idx].iov_base) {
> > +            iov.iov_len += f->iov[idx].iov_len;
> > +            continue;
> > +        }
> > +        if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
> > +            error_report("migrate: madvise DONTNEED failed %p %ld: %s",
> > +                         iov.iov_base, iov.iov_len, strerror(errno));
> > +        }
> > +        iov = f->iov[idx];
> > +    }
> > +    if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
> > +            error_report("migrate: madvise DONTNEED failed %p %ld: %s",
> > +                         iov.iov_base, iov.iov_len, strerror(errno));
> > +    }
> > +    memset(f->may_free, 0, sizeof(f->may_free));
> > +}
> > +
> >  /**
> >   * Flushes QEMUFile buffer
> >   *
> > @@ -151,6 +187,8 @@ void qemu_fflush(QEMUFile *f)
> >      if (f->iovcnt > 0) {
> >          expect = iov_size(f->iov, f->iovcnt);
> >          ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos);
> > +
> > +        qemu_iovec_release_ram(f);
> >      }
> >  
> >      if (ret >= 0) {
> > @@ -304,13 +342,19 @@ int qemu_fclose(QEMUFile *f)
> >      return ret;
> >  }
> >  
> > -static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size)
> > +static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
> > +                         bool may_free)
> >  {
> >      /* check for adjacent buffer and coalesce them */
> >      if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
> > -        f->iov[f->iovcnt - 1].iov_len) {
> > +        f->iov[f->iovcnt - 1].iov_len &&
> > +        may_free == test_bit(f->iovcnt - 1, f->may_free))
> > +    {
> >          f->iov[f->iovcnt - 1].iov_len += size;
> >      } else {
> > +        if (may_free) {
> > +            set_bit(f->iovcnt, f->may_free);
> > +        }
> >          f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
> >          f->iov[f->iovcnt++].iov_len = size;
> >      }
> > @@ -320,14 +364,15 @@ static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size)
> >      }
> >  }
> >  
> > -void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size)
> > +void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
> > +                           bool may_free)
> >  {
> >      if (f->last_error) {
> >          return;
> >      }
> >  
> >      f->bytes_xfer += size;
> > -    add_to_iovec(f, buf, size);
> > +    add_to_iovec(f, buf, size, may_free);
> >  }
> >  
> >  void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
> > @@ -345,7 +390,7 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
> >          }
> >          memcpy(f->buf + f->buf_index, buf, l);
> >          f->bytes_xfer += l;
> > -        add_to_iovec(f, f->buf + f->buf_index, l);
> > +        add_to_iovec(f, f->buf + f->buf_index, l, false);
> >          f->buf_index += l;
> >          if (f->buf_index == IO_BUF_SIZE) {
> >              qemu_fflush(f);
> > @@ -366,7 +411,7 @@ void qemu_put_byte(QEMUFile *f, int v)
> >  
> >      f->buf[f->buf_index] = v;
> >      f->bytes_xfer++;
> > -    add_to_iovec(f, f->buf + f->buf_index, 1);
> > +    add_to_iovec(f, f->buf + f->buf_index, 1, false);
> >      f->buf_index++;
> >      if (f->buf_index == IO_BUF_SIZE) {
> >          qemu_fflush(f);
> > @@ -647,7 +692,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
> >      }
> >      qemu_put_be32(f, blen);
> >      if (f->ops->writev_buffer) {
> > -        add_to_iovec(f, f->buf + f->buf_index, blen);
> > +        add_to_iovec(f, f->buf + f->buf_index, blen, false);
> >      }
> >      f->buf_index += blen;
> >      if (f->buf_index == IO_BUF_SIZE) {
> > diff --git a/migration/ram.c b/migration/ram.c
> > index d866b6518b..5a43f716d1 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -726,6 +726,16 @@ static int save_zero_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset,
> >      return pages;
> >  }
> >  
> > +static void ram_release_pages(MigrationState *ms, const char *block_name,
> > +                              uint64_t offset, int pages)
> > +{
> > +    if (!migrate_release_ram() || !migration_in_postcopy(ms)) {
> > +        return;
> > +    }
> > +
> > +    ram_discard_range(NULL, block_name, offset, pages << TARGET_PAGE_BITS);
> > +}
> > +
> >  /**
> >   * ram_save_page: Send the given page to the stream
> >   *
> > @@ -786,6 +796,7 @@ static int ram_save_page(MigrationState *ms, QEMUFile *f, PageSearchStatus *pss,
> >               * page would be stale
> >               */
> >              xbzrle_cache_zero_page(current_addr);
> > +            ram_release_pages(ms, block->idstr, pss->offset, pages);
> >          } else if (!ram_bulk_stage &&
> >                     !migration_in_postcopy(ms) && migrate_use_xbzrle()) {
> >              pages = save_xbzrle_page(f, &p, current_addr, block,
> > @@ -804,7 +815,9 @@ static int ram_save_page(MigrationState *ms, QEMUFile *f, PageSearchStatus *pss,
> >          *bytes_transferred += save_page_header(f, block,
> >                                                 offset | RAM_SAVE_FLAG_PAGE);
> >          if (send_async) {
> > -            qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE);
> > +            qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE,
> > +                                  migrate_release_ram() &
> > +                                  migration_in_postcopy(ms));
> >          } else {
> >              qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> >          }
> > @@ -834,6 +847,8 @@ static int do_compress_ram_page(QEMUFile *f, RAMBlock *block,
> >          error_report("compressed data failed!");
> >      } else {
> >          bytes_sent += blen;
> > +        ram_release_pages(migrate_get_current(), block->idstr,
> > +                          offset & TARGET_PAGE_MASK, 1);
> >      }
> >  
> >      return bytes_sent;
> > @@ -973,12 +988,17 @@ static int ram_save_compressed_page(MigrationState *ms, QEMUFile *f,
> >                      error_report("compressed data failed!");
> >                  }
> >              }
> > +            if (pages > 0) {
> > +                ram_release_pages(ms, block->idstr, pss->offset, pages);
> > +            }
> >          } else {
> >              offset |= RAM_SAVE_FLAG_CONTINUE;
> >              pages = save_zero_page(f, block, offset, p, bytes_transferred);
> >              if (pages == -1) {
> >                  pages = compress_page_with_multi_thread(f, block, offset,
> >                                                          bytes_transferred);
> > +            } else {
> > +                ram_release_pages(ms, block->idstr, pss->offset, pages);
> >              }
> >          }
> >      }
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 82fabc6e24..e58228d083 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -865,11 +865,14 @@
> >  #        side, this process is called COarse-Grain LOck Stepping (COLO) for
> >  #        Non-stop Service. (since 2.8)
> >  #
> > +# @release-ram: if enabled, qemu will free the migrated ram pages on the source
> > +#        during postcopy-ram migration. (since 2.9)
> > +#
> >  # Since: 1.2
> >  ##
> >  { 'enum': 'MigrationCapability',
> >    'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
> > -           'compress', 'events', 'postcopy-ram', 'x-colo'] }
> > +           'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram'] }
> >  
> >  ##
> >  # @MigrationCapabilityStatus:
> > -- 
> > 2.11.0
> > 
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK