Re: [PATCH 1/3] multifd: Add colo support

[Peter Xu <peterx@redhat.com>]

On Tue, Dec 30, 2025 at 03:05:44PM +0100, Lukas Straub wrote:
> Like in the normal ram_load() path, put the received pages into the
> colo cache and mark the pages in the bitmap so that they will be
> flushed to the guest later.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> ---
>  migration/meson.build    |  2 +-
>  migration/multifd-colo.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
>  migration/multifd-colo.h | 26 ++++++++++++++++++++++
>  migration/multifd.c      | 14 +++++++++---
>  4 files changed, 95 insertions(+), 4 deletions(-)
> 
> diff --git a/migration/meson.build b/migration/meson.build
> index 16909d54c5110fc5d8187fd3a68c4a5b08b59ea7..1e59fe4f1f0bbfffed90df38e8f39fa87bceb9b9 100644
> --- a/migration/meson.build
> +++ b/migration/meson.build
> @@ -40,7 +40,7 @@ system_ss.add(files(
>  ), gnutls, zlib)
>  
>  if get_option('replication').allowed()
> -  system_ss.add(files('colo-failover.c', 'colo.c'))
> +  system_ss.add(files('colo-failover.c', 'colo.c', 'multifd-colo.c'))
>  else
>    system_ss.add(files('colo-stubs.c'))
>  endif
> diff --git a/migration/multifd-colo.c b/migration/multifd-colo.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..05a81e57b2bda517cbc0844b4f03dc78453f6af8
> --- /dev/null
> +++ b/migration/multifd-colo.c
> @@ -0,0 +1,57 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + *
> + * multifd colo implementation
> + *
> + * Copyright (c) Lukas Straub <lukasstraub2@web.de>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "exec/target_page.h"
> +#include "qemu/error-report.h"
> +#include "qapi/error.h"
> +#include "ram.h"
> +#include "multifd.h"
> +#include "options.h"
> +#include "io/channel-socket.h"
> +#include "migration/colo.h"
> +#include "multifd-colo.h"
> +#include "system/ramblock.h"
> +
> +void multifd_colo_prepare_recv(MultiFDRecvParams *p)
> +{
> +    if (!migrate_colo()) {

We should avoid invoking *_colo_*() function, then check COLO enabled or
not only reaching here.  Instead, we'd check "migrate_colo()" first and
invoke it only if it's enabled.

> +        return;
> +    }
> +
> +    assert(p->block->colo_cache);
> +
> +    /*
> +     * While we're still in precopy state (not yet in colo state), we copy
> +     * received pages to both guest and cache. No need to set dirty bits,
> +     * since guest and cache memory are in sync.
> +     */
> +    if (migration_incoming_in_colo_state()) {
> +        colo_record_bitmap(p->block, p->normal, p->normal_num);
> +    }
> +    p->host = p->block->colo_cache;

May want to update the comment of "host" then, because it isn't always
pointing to ramblock's buffer now when COLO is enabled.

> +}
> +
> +void multifd_colo_process_recv(MultiFDRecvParams *p)
> +{
> +    if (!migrate_colo()) {

Same here.

> +        return;
> +    }
> +
> +    if (!migration_incoming_in_colo_state()) {
> +        for (int i = 0; i < p->normal_num; i++) {
> +            void *guest = p->block->host + p->normal[i];
> +            void *cache = p->host + p->normal[i];
> +            memcpy(guest, cache, multifd_ram_page_size());
> +        }
> +    }
> +    p->host = p->block->host;
> +}
> diff --git a/migration/multifd-colo.h b/migration/multifd-colo.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..82eaf3f48c47de2f090f9de52f9d57a337d4754a
> --- /dev/null
> +++ b/migration/multifd-colo.h
> @@ -0,0 +1,26 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + *
> + * multifd colo header
> + *
> + * Copyright (c) Lukas Straub <lukasstraub2@web.de>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#ifndef QEMU_MIGRATION_MULTIFD_COLO_H
> +#define QEMU_MIGRATION_MULTIFD_COLO_H
> +
> +#ifdef CONFIG_REPLICATION
> +
> +void multifd_colo_prepare_recv(MultiFDRecvParams *p);
> +void multifd_colo_process_recv(MultiFDRecvParams *p);
> +
> +#else
> +
> +static inline void multifd_colo_prepare_recv(MultiFDRecvParams *p) {}
> +static inline void multifd_colo_process_recv(MultiFDRecvParams *p) {}
> +
> +#endif
> +#endif
> diff --git a/migration/multifd.c b/migration/multifd.c
> index bf6da85af8a1e207235ce06b8dbace33beded6d8..9006f73cc5b52e8814da107c0b5c867ee6d03a95 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -29,6 +29,7 @@
>  #include "qemu-file.h"
>  #include "trace.h"
>  #include "multifd.h"
> +#include "multifd-colo.h"
>  #include "threadinfo.h"
>  #include "options.h"
>  #include "qemu/yank.h"
> @@ -1398,11 +1399,18 @@ static void *multifd_recv_thread(void *opaque)
>              if (is_device_state) {
>                  assert(use_packets);
>                  ret = multifd_device_state_recv(p, &local_err);
> +                if (ret != 0) {
> +                    break;
> +                }
>              } else {
> +                multifd_colo_prepare_recv(p);
> +
>                  ret = multifd_recv_state->ops->recv(p, &local_err);
> -            }
> -            if (ret != 0) {
> -                break;
> +                if (ret != 0) {
> +                    break;
> +                }
> +
> +                multifd_colo_process_recv(p);

Personally I'd suggest we introduce multifd_ram_state_recv() and put
everything there.

Thanks,

>              }
>          } else if (is_device_state) {
>              error_setg(&local_err,
> 
> -- 
> 2.39.5
> 

-- 
Peter Xu