migration/savevm: use stack-allocated bitmap in configuration_validate_capabilities

configuration_validate_capabilities() allocates a bitmap on the heap
to track source capabilities via bitmap_new()/g_free().  Since
MIGRATION_CAPABILITY__MAX is a small compile-time constant (< 64),
a heap allocation for a bitmap this small is wasteful: it adds
malloc/free overhead and a potential cache miss for a transient
8-byte allocation.

Replace with DECLARE_BITMAP() on the stack and bitmap_zero() to
initialize.  This eliminates the heap round-trip entirely.

Signed-off-by: Bin Guo <guobin@linux.alibaba.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20260518110112.21395-5-guobin@linux.alibaba.com
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/migration/savevm.c b/migration/savevm.c
index d1dd696c17793476db51b81dc83869260899fb88..23adaf9dd9263b8dafe808f0637724fe4a5482b2 100644 (file)
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -347,10 +347,10 @@ static bool configuration_validate_capabilities(SaveState *state)
 {
     bool ret = true;
     MigrationState *s = migrate_get_current();
-    unsigned long *source_caps_bm;
+    DECLARE_BITMAP(source_caps_bm, MIGRATION_CAPABILITY__MAX);
     int i;
 
-    source_caps_bm = bitmap_new(MIGRATION_CAPABILITY__MAX);
+    bitmap_zero(source_caps_bm, MIGRATION_CAPABILITY__MAX);
     for (i = 0; i < state->caps_count; i++) {
         MigrationCapability capability = state->capabilities[i];
         set_bit(capability, source_caps_bm);
@@ -373,7 +373,6 @@ static bool configuration_validate_capabilities(SaveState *state)
         }
     }
 
-    g_free(source_caps_bm);
     return ret;
 }