Add a new cap to allow mapping hugetlbfs backed RAMs in small page sizes.
Signed-off-by: Peter Xu <pet...@redhat.com>
---
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
