* Peter Xu (pet...@redhat.com) wrote:
> Multifd thread model does not work for compression, explicitly disable it.
>
> Note that previuosly even we can enable both of them, nothing will go
> wrong, because the compression code has higher priority so multifd feature
> will just be ignored. Now we'll fail even earlier at config time so the
> user should be aware of the consequence better.
>
> Note that there can be a slight chance of breaking existing users, but
> let's assume they're not majority and not serious users, or they should
> have found that multifd is not working already.
>
> With that, we can safely drop the check in ram_save_target_page() for using
> multifd, because when multifd=on then compression=off, then the removed
> check on save_page_use_compression() will also always return false too.
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
Yes, and of course if they were trying to use it, they should have been
trying to use multifd-compression parameter instead, which is different
code.
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> migration/migration.c | 7 +++++++
> migration/ram.c | 11 +++++------
> 2 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 844bca1ff6..ef00bff0b3 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1349,6 +1349,13 @@ static bool migrate_caps_check(bool *cap_list,
> }
> }
>
> + if (cap_list[MIGRATION_CAPABILITY_MULTIFD]) {
> + if (cap_list[MIGRATION_CAPABILITY_COMPRESS]) {
> + error_setg(errp, "Multifd is not compatible with compress");
> + return false;
> + }
> + }
> +
> return true;
> }
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 1d42414ecc..1338e47665 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2305,13 +2305,12 @@ static int ram_save_target_page(RAMState *rs,
> PageSearchStatus *pss)
> }
>
> /*
> - * Do not use multifd for:
> - * 1. Compression as the first page in the new block should be posted out
> - * before sending the compressed page
> - * 2. In postcopy as one whole host page should be placed
> + * Do not use multifd in postcopy as one whole host page should be
> + * placed. Meanwhile postcopy requires atomic update of pages, so even
> + * if host page size == guest page size the dest guest during run may
> + * still see partially copied pages which is data corruption.
> */
> - if (!save_page_use_compression(rs) && migrate_use_multifd()
> - && !migration_in_postcopy()) {
> + if (migrate_use_multifd() && !migration_in_postcopy()) {
> return ram_save_multifd_page(rs, block, offset);
> }
>
> --
> 2.37.3
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
