* Peter Xu (pet...@redhat.com) wrote:
> Add a new cap to allow mapping hugetlbfs backed RAMs in small page sizes.
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
although, I'm curious if the protocol actually changes - or whether
a doublepage enabled destination would work with an unmodified source?
I guess potentially you can get away without the dirty clearing of the
partially sent hugepages that the source normally does.
Dave
> ---
> migration/migration.c | 48 ++++++++++++++++++++++++++++++++++++++++++-
> migration/migration.h | 1 +
> qapi/migration.json | 7 ++++++-
> 3 files changed, 54 insertions(+), 2 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 64f74534e2..b174f2af92 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -17,6 +17,7 @@
> #include "qemu/cutils.h"
> #include "qemu/error-report.h"
> #include "qemu/main-loop.h"
> +#include "qemu/madvise.h"
> #include "migration/blocker.h"
> #include "exec.h"
> #include "fd.h"
> @@ -62,6 +63,7 @@
> #include "sysemu/cpus.h"
> #include "yank_functions.h"
> #include "sysemu/qtest.h"
> +#include "exec/ramblock.h"
>
> #define MAX_THROTTLE (128 << 20) /* Migration transfer speed
> throttling */
>
> @@ -1363,12 +1365,47 @@ static bool migrate_caps_check(bool *cap_list,
> "Zero copy only available for non-compressed non-TLS
> multifd migration");
> return false;
> }
> +
> + if (cap_list[MIGRATION_CAPABILITY_HUGETLB_DOUBLEMAP]) {
> + RAMBlock *rb;
> +
> + /* Check whether the platform/binary supports the new madvise()s */
> +
> +#if QEMU_MADV_SPLIT == QEMU_MADV_INVALID
> + error_setg(errp, "MADV_SPLIT is not supported by the QEMU binary");
> + return false;
> +#endif
> +
> +#if QEMU_MADV_COLLAPSE == QEMU_MADV_INVALID
> + error_setg(errp, "MADV_COLLAPSE is not supported by the QEMU
> binary");
> + return false;
> +#endif
> +
> + /*
> + * Check against kernel support of MADV_SPLIT is not easy, delay
> + * that until we have all the hugetlb mappings ready on dest node,
> + * meanwhile do the best effort check here because doublemap
> + * requires the hugetlb ramblocks to be shared first.
> + */
> + RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
> + if (qemu_ram_is_hugetlb(rb) && !qemu_ram_is_shared(rb)) {
> + error_setg(errp, "RAMBlock '%s' needs to be shared for
> doublemap",
> + rb->idstr);
> + return false;
> + }
> + }
> + }
> #else
> if (cap_list[MIGRATION_CAPABILITY_ZERO_COPY_SEND]) {
> error_setg(errp,
> "Zero copy currently only available on Linux");
> return false;
> }
> +
> + if (cap_list[MIGRATION_CAPABILITY_HUGETLB_DOUBLEMAP]) {
> + error_setg(errp, "Hugetlb doublemap is only supported on Linux");
> + return false;
> + }
> #endif
>
> if (cap_list[MIGRATION_CAPABILITY_POSTCOPY_PREEMPT]) {
> @@ -2792,6 +2829,13 @@ bool migrate_postcopy_preempt(void)
> return s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_PREEMPT];
> }
>
> +bool migrate_hugetlb_doublemap(void)
> +{
> + MigrationState *s = migrate_get_current();
> +
> + return s->enabled_capabilities[MIGRATION_CAPABILITY_HUGETLB_DOUBLEMAP];
> +}
> +
> /* migration thread support */
> /*
> * Something bad happened to the RP stream, mark an error
> @@ -4472,7 +4516,9 @@ static Property migration_properties[] = {
> DEFINE_PROP_MIG_CAP("x-return-path", MIGRATION_CAPABILITY_RETURN_PATH),
> DEFINE_PROP_MIG_CAP("x-multifd", MIGRATION_CAPABILITY_MULTIFD),
> DEFINE_PROP_MIG_CAP("x-background-snapshot",
> - MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT),
> + MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT),
> + DEFINE_PROP_MIG_CAP("hugetlb-doublemap",
> + MIGRATION_CAPABILITY_HUGETLB_DOUBLEMAP),
> #ifdef CONFIG_LINUX
> DEFINE_PROP_MIG_CAP("x-zero-copy-send",
> MIGRATION_CAPABILITY_ZERO_COPY_SEND),
> diff --git a/migration/migration.h b/migration/migration.h
> index 5674a13876..bbd610a2d5 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -447,6 +447,7 @@ bool migrate_use_events(void);
> bool migrate_postcopy_blocktime(void);
> bool migrate_background_snapshot(void);
> bool migrate_postcopy_preempt(void);
> +bool migrate_hugetlb_doublemap(void);
>
> /* Sending on the return path - generic and then for each message type */
> void migrate_send_rp_shut(MigrationIncomingState *mis,
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 88ecf86ac8..b23516e75e 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -477,6 +477,11 @@
> # will be handled faster. This is a performance feature
> and
> # should not affect the correctness of postcopy migration.
> # (since 7.1)
> +# @hugetlb-doublemap: If enabled, the migration process will allow postcopy
> +# to handle page faults based on small pages even if
> +# hugetlb is used. This will drastically reduce page
> +# fault latencies when hugetlb is used as the guest RAM
> +# backends. (since 7.3)
> #
> # Features:
> # @unstable: Members @x-colo and @x-ignore-shared are experimental.
> @@ -492,7 +497,7 @@
> 'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
> { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
> 'validate-uuid', 'background-snapshot',
> - 'zero-copy-send', 'postcopy-preempt'] }
> + 'zero-copy-send', 'postcopy-preempt', 'hugetlb-doublemap'] }
>
> ##
> # @MigrationCapabilityStatus:
> --
> 2.37.3
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
