[PULL 17/18] tests: add unit tests for RamDiscardManager multi-source aggregation

[Peter Xu <peterx@redhat.com>]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Add various unit tests for the RamDiscardManager multi-source
aggregation functionality.

The test uses a TestRamDiscardSource QOM object that tracks populated
state via a bitmap, similar to RamBlockAttributes implementation.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Link: https://lore.kernel.org/r/20260604-rdm5-v5-10-5768e6a0943d@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 MAINTAINERS                                 |    2 +
 tests/unit/test-ram-discard-manager-stubs.c |   48 +
 tests/unit/test-ram-discard-manager.c       | 1235 +++++++++++++++++++
 tests/unit/meson.build                      |    8 +-
 4 files changed, 1292 insertions(+), 1 deletion(-)
 create mode 100644 tests/unit/test-ram-discard-manager-stubs.c
 create mode 100644 tests/unit/test-ram-discard-manager.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 18b659a44c..fc6d035d4c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3363,6 +3363,8 @@ F: system/memory-internal.h
 F: system/ram-block-attributes.c
 F: system/ram-discard-manager.c
 F: scripts/coccinelle/memory-region-housekeeping.cocci
+F: tests/unit/test-ram-discard-manager.c
+F: tests/unit/test-ram-discard-manager-stubs.c
 
 Memory devices
 M: David Hildenbrand <david@kernel.org>
diff --git a/tests/unit/test-ram-discard-manager-stubs.c b/tests/unit/test-ram-discard-manager-stubs.c
new file mode 100644
index 0000000000..74b126fd3f
--- /dev/null
+++ b/tests/unit/test-ram-discard-manager-stubs.c
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#include "qemu/osdep.h"
+#include "qom/object.h"
+#include "glib.h"
+#include "system/memory.h"
+
+RamDiscardManager *memory_region_get_ram_discard_manager(MemoryRegion *mr)
+{
+    return mr->rdm;
+}
+
+int memory_region_add_ram_discard_source(MemoryRegion *mr,
+                                         RamDiscardSource *source)
+{
+    if (!mr->rdm) {
+        mr->rdm = ram_discard_manager_new(mr);
+    }
+    return ram_discard_manager_add_source(mr->rdm, source);
+}
+
+int memory_region_del_ram_discard_source(MemoryRegion *mr,
+                                         RamDiscardSource *source)
+{
+    RamDiscardManager *rdm = mr->rdm;
+
+    if (!rdm) {
+        return 0;
+    }
+
+    return ram_discard_manager_del_source(rdm, source);
+}
+
+uint64_t memory_region_size(const MemoryRegion *mr)
+{
+    return int128_get64(mr->size);
+}
+
+MemoryRegionSection *memory_region_section_new_copy(MemoryRegionSection *s)
+{
+    MemoryRegionSection *copy = g_new(MemoryRegionSection, 1);
+    *copy = *s;
+    return copy;
+}
+
+void memory_region_section_free_copy(MemoryRegionSection *s)
+{
+    g_free(s);
+}
diff --git a/tests/unit/test-ram-discard-manager.c b/tests/unit/test-ram-discard-manager.c
new file mode 100644
index 0000000000..3d39a1e94b
--- /dev/null
+++ b/tests/unit/test-ram-discard-manager.c
@@ -0,0 +1,1235 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#include "qemu/osdep.h"
+#include "qemu/bitmap.h"
+#include "qemu/module.h"
+#include "qemu/main-loop.h"
+#include "qapi/error.h"
+#include "qom/object.h"
+#include "qom/qom-qobject.h"
+#include "glib.h"
+#include "system/memory.h"
+
+#define TYPE_TEST_RAM_DISCARD_SOURCE "test-ram-discard-source"
+
+OBJECT_DECLARE_SIMPLE_TYPE(TestRamDiscardSource, TEST_RAM_DISCARD_SOURCE)
+
+struct TestRamDiscardSource {
+    Object parent;
+
+    MemoryRegion *mr;
+    uint64_t granularity;
+    unsigned long *bitmap;
+    uint64_t bitmap_size;
+};
+
+static uint64_t test_rds_get_min_granularity(const RamDiscardSource *rds,
+                                             const MemoryRegion *mr)
+{
+    TestRamDiscardSource *src = TEST_RAM_DISCARD_SOURCE(rds);
+
+    g_assert(mr == src->mr);
+    return src->granularity;
+}
+
+static bool test_rds_is_populated(const RamDiscardSource *rds,
+                                  const MemoryRegionSection *section)
+{
+    TestRamDiscardSource *src = TEST_RAM_DISCARD_SOURCE(rds);
+    uint64_t offset = section->offset_within_region;
+    uint64_t size = int128_get64(section->size);
+    uint64_t first_bit = offset / src->granularity;
+    uint64_t last_bit = (offset + size - 1) / src->granularity;
+    unsigned long found;
+
+    g_assert(section->mr == src->mr);
+
+    /* Check if any bit in range is zero (discarded) */
+    found = find_next_zero_bit(src->bitmap, last_bit + 1, first_bit);
+    return found > last_bit;
+}
+
+static void test_rds_class_init(ObjectClass *klass, const void *data)
+{
+    RamDiscardSourceClass *rdsc = RAM_DISCARD_SOURCE_CLASS(klass);
+
+    rdsc->get_min_granularity = test_rds_get_min_granularity;
+    rdsc->is_populated = test_rds_is_populated;
+}
+
+static const TypeInfo test_rds_info = {
+    .name = TYPE_TEST_RAM_DISCARD_SOURCE,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(TestRamDiscardSource),
+    .class_init = test_rds_class_init,
+    .interfaces = (const InterfaceInfo[]) {
+        { TYPE_RAM_DISCARD_SOURCE },
+        { }
+    },
+};
+
+static TestRamDiscardSource *test_source_new(MemoryRegion *mr,
+                                             uint64_t granularity)
+{
+    TestRamDiscardSource *src;
+    uint64_t region_size = memory_region_size(mr);
+
+    src = TEST_RAM_DISCARD_SOURCE(object_new(TYPE_TEST_RAM_DISCARD_SOURCE));
+    src->mr = mr;
+    src->granularity = granularity;
+    src->bitmap_size = DIV_ROUND_UP(region_size, granularity);
+    src->bitmap = bitmap_new(src->bitmap_size);
+
+    return src;
+}
+
+static void test_source_free(TestRamDiscardSource *src)
+{
+    g_free(src->bitmap);
+    object_unref(OBJECT(src));
+}
+
+static void test_source_populate(TestRamDiscardSource *src,
+                                 uint64_t offset, uint64_t size)
+{
+    uint64_t first_bit = offset / src->granularity;
+    uint64_t nbits = size / src->granularity;
+
+    bitmap_set(src->bitmap, first_bit, nbits);
+}
+
+static void test_source_discard(TestRamDiscardSource *src,
+                                uint64_t offset, uint64_t size)
+{
+    uint64_t first_bit = offset / src->granularity;
+    uint64_t nbits = size / src->granularity;
+
+    bitmap_clear(src->bitmap, first_bit, nbits);
+}
+
+typedef struct TestListener {
+    RamDiscardListener rdl;
+    int populate_count;
+    int discard_count;
+    uint64_t last_populate_offset;
+    uint64_t last_populate_size;
+    uint64_t last_discard_offset;
+    uint64_t last_discard_size;
+    int fail_on_populate;  /* Return error on Nth populate */
+    int populate_call_num;
+} TestListener;
+
+static int test_listener_populate(RamDiscardListener *rdl,
+                                  const MemoryRegionSection *section)
+{
+    TestListener *tl = container_of(rdl, TestListener, rdl);
+
+    tl->populate_call_num++;
+    if (tl->fail_on_populate > 0 &&
+        tl->populate_call_num >= tl->fail_on_populate) {
+        return -ENOMEM;
+    }
+
+    tl->populate_count++;
+    tl->last_populate_offset = section->offset_within_region;
+    tl->last_populate_size = int128_get64(section->size);
+    return 0;
+}
+
+static void test_listener_discard(RamDiscardListener *rdl,
+                                  const MemoryRegionSection *section)
+{
+    TestListener *tl = container_of(rdl, TestListener, rdl);
+
+    tl->discard_count++;
+    tl->last_discard_offset = section->offset_within_region;
+    tl->last_discard_size = int128_get64(section->size);
+}
+
+static void test_listener_init(TestListener *tl)
+{
+    ram_discard_listener_init(&tl->rdl,
+        test_listener_populate,
+        test_listener_discard);
+}
+
+#define TEST_REGION_SIZE (16 * 1024 * 1024)  /* 16 MB */
+#define GRANULARITY_4K   (4 * 1024)
+#define GRANULARITY_2M   (2 * 1024 * 1024)
+
+static MemoryRegion *test_mr;
+
+static void test_setup(void)
+{
+    test_mr = g_new0(MemoryRegion, 1);
+    test_mr->size = int128_make64(TEST_REGION_SIZE);
+    test_mr->ram = true;
+}
+
+static void test_teardown(void)
+{
+    g_clear_pointer(&test_mr->rdm, object_unref);
+    object_unparent(OBJECT(test_mr));
+    g_free(test_mr);
+    test_mr = NULL;
+}
+
+static void test_single_source_basic(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+    g_assert_null(rdm);
+
+    /* Add source */
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+    g_assert_nonnull(rdm);
+
+    g_assert_cmpuint(ram_discard_manager_get_min_granularity(rdm, test_mr),
+                     ==, GRANULARITY_4K);
+
+    /* Initially all discarded */
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(GRANULARITY_4K);
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate a range in source */
+    test_source_populate(src, 0, GRANULARITY_4K * 4);
+
+    /* Now should be populated */
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Check larger section */
+    section.size = int128_make64(GRANULARITY_4K * 4);
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Check section that spans populated and discarded */
+    section.size = int128_make64(GRANULARITY_4K * 8);
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    test_source_free(src);
+    test_teardown();
+}
+
+static void test_single_source_listener(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Populate some ranges before adding listener */
+    test_source_populate(src, 0, GRANULARITY_4K * 4);
+    test_source_populate(src, GRANULARITY_4K * 8, GRANULARITY_4K * 4);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+    g_assert_nonnull(rdm);
+
+    /* Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Should have been notified about populated regions */
+    g_assert_cmpint(tl.populate_count, ==, 2);
+
+    /* Notify populate for new range */
+    tl.populate_count = 0;
+    test_source_populate(src, GRANULARITY_4K * 16, GRANULARITY_4K * 2);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              GRANULARITY_4K * 16,
+                                              GRANULARITY_4K * 2);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_offset, ==, GRANULARITY_4K * 16);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 2);
+
+    /* Notify discard */
+    tl.discard_count = 0;
+    test_source_discard(src, 0, GRANULARITY_4K * 4);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src),
+                                       0, GRANULARITY_4K * 4);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+    g_assert_cmpuint(tl.last_discard_offset, ==, 0);
+    g_assert_cmpuint(tl.last_discard_size, ==, GRANULARITY_4K * 4);
+
+    /* Unregister listener */
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+static void test_two_sources_same_granularity(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Add first source */
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+
+    /* Add second source */
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+    g_assert_nonnull(rdm);
+
+    /* Check granularity */
+    g_assert_cmpuint(ram_discard_manager_get_min_granularity(rdm, test_mr),
+                     ==, GRANULARITY_4K);
+
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(GRANULARITY_4K);
+
+    /* Both discarded -> aggregated discarded */
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate in src1 only */
+    test_source_populate(src1, 0, GRANULARITY_4K);
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate in src2 only */
+    test_source_discard(src1, 0, GRANULARITY_4K);
+    test_source_populate(src2, 0, GRANULARITY_4K);
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate in both -> aggregated populated */
+    test_source_populate(src1, 0, GRANULARITY_4K);
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Remove sources */
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Two sources with different granularities (4K and 2M).
+ * The aggregated granularity should be GCD(4K, 2M) = 4K.
+ */
+static void test_two_sources_different_granularity(void)
+{
+    TestRamDiscardSource *src_4k, *src_2m;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    int ret;
+
+    test_setup();
+
+    src_4k = test_source_new(test_mr, GRANULARITY_4K);
+    src_2m = test_source_new(test_mr, GRANULARITY_2M);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src_4k));
+    g_assert_cmpint(ret, ==, 0);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src_2m));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    g_assert_cmpuint(ram_discard_manager_get_min_granularity(rdm, test_mr),
+                     ==, GRANULARITY_4K);
+
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(GRANULARITY_4K);
+
+    /* Both discarded */
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate 4K in src_4k, but src_2m still discarded the whole 2M block */
+    test_source_populate(src_4k, 0, GRANULARITY_4K);
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate 2M in src_2m (which includes the 4K block) */
+    test_source_populate(src_2m, 0, GRANULARITY_2M);
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Check a 4K block at offset 4K (populated in src_2m but not in src_4k) */
+    section.offset_within_region = GRANULARITY_4K;
+    g_assert_false(ram_discard_manager_is_populated(rdm, &section));
+
+    /* Populate it in src_4k */
+    test_source_populate(src_4k, GRANULARITY_4K, GRANULARITY_4K);
+    g_assert_true(ram_discard_manager_is_populated(rdm, &section));
+
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src_2m));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src_4k));
+
+    test_source_free(src_2m);
+    test_source_free(src_4k);
+    test_teardown();
+}
+
+/*
+ * Test: Notification with two sources.
+ * Populate notification should only fire when all sources are populated.
+ */
+static void test_two_sources_notification(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* No populate notifications yet (all discarded) */
+    g_assert_cmpint(tl.populate_count, ==, 0);
+
+    /* Populate in src1 only - no notification (src2 still discarded) */
+    test_source_populate(src1, 0, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src1),
+                                              0, GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl.populate_count, ==, 0);
+
+    /* Populate same range in src2 - now should notify */
+    test_source_populate(src2, 0, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src2),
+                                              0, GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl.populate_count, ==, 1);
+
+    /* Discard from src1 - should notify discard immediately */
+    tl.discard_count = 0;
+    test_source_discard(src1, 0, GRANULARITY_4K * 2);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src1),
+                                       0, GRANULARITY_4K * 2);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Adding source with existing listener.
+ * When a new source is added, listeners should be notified about
+ * regions that become discarded.
+ */
+static void test_add_source_with_listener(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Populate some range in src1 */
+    test_source_populate(src1, 0, GRANULARITY_4K * 8);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Should have been notified about populated region */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpint(tl.last_populate_offset, ==, 0);
+    g_assert_cmpint(tl.last_populate_size, ==, GRANULARITY_4K * 8);
+
+    /* src2 has part of the region populated, part discarded */
+    /* src2 has 0-4 populated, 4-8 discarded */
+    test_source_populate(src2, 0, GRANULARITY_4K * 4);
+
+    /* Add src2 - listener should be notified about newly discarded regions */
+    tl.discard_count = 0;
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    /*
+     * The range 4K*4 to 4K*8 was populated in src1 but discarded in src2,
+     * so it becomes aggregated-discarded. Listener should be notified.
+     * Only this range should trigger a discard notification - regions beyond
+     * 4K*8 were already discarded in src1, so adding src2 doesn't change them.
+     */
+    g_assert_cmpint(tl.discard_count, ==, 1);
+    g_assert_cmpint(tl.last_discard_offset, ==, GRANULARITY_4K * 4);
+    g_assert_cmpint(tl.last_discard_size, ==, GRANULARITY_4K * 4);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Removing source with existing listener.
+ * When a source is removed, listeners should be notified about
+ * regions that become populated.
+ */
+static void test_remove_source_with_listener(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* src1: all of first 8 blocks populated */
+    test_source_populate(src1, 0, GRANULARITY_4K * 8);
+    /* src2: only first 4 blocks populated */
+    test_source_populate(src2, 0, GRANULARITY_4K * 4);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Only first 4 blocks are aggregated-populated */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 4);
+
+    /* Remove src2 - blocks 4-8 should become populated */
+    tl.populate_count = 0;
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+
+    /* Listener should be notified about newly populated region (4K*4 to 4K*8) */
+    g_assert_cmpint(tl.populate_count, >=, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Add a source, register a listener, remove the source, then add it back.
+ * This checks the transition from 0 sources (all populated) to 1 source
+ * (partially discarded) with an active listener.
+ */
+static void test_readd_source_with_listener(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Populate some range in src */
+    test_source_populate(src, 0, GRANULARITY_4K * 8);
+
+    /* 1. Add source */
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* 2. Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Listener notified about populated region (0 - 32K) */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 8);
+
+    /* 3. Remove source */
+    tl.populate_count = 0;
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+
+    /*
+     * With 0 sources, everything is populated.
+     * The range that was discarded in src (from 32K to end) becomes populated.
+     */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_offset, ==, GRANULARITY_4K * 8);
+    g_assert_cmpuint(tl.last_populate_size, ==, TEST_REGION_SIZE - GRANULARITY_4K * 8);
+
+    /* 4. Add source back */
+    tl.discard_count = 0;
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+
+    /*
+     * Now we have 1 source again. The range (32K to end) is discarded again.
+     * Listener should be notified about this discard.
+     */
+    g_assert_cmpint(tl.discard_count, ==, 1);
+    g_assert_cmpuint(tl.last_discard_offset, ==, GRANULARITY_4K * 8);
+    g_assert_cmpuint(tl.last_discard_size, ==, TEST_REGION_SIZE - GRANULARITY_4K * 8);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Duplicate source registration should fail.
+ */
+static void test_duplicate_source(void)
+{
+    TestRamDiscardSource *src;
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+
+    /* Adding same source again should fail */
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, -EBUSY);
+
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Populate notification rollback on listener error.
+ */
+static void test_populate_rollback(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl1 = { 0, }, tl2 = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register two listeners */
+    test_listener_init(&tl1);
+    test_listener_init(&tl2);
+    tl2.fail_on_populate = 1;  /* Second listener fails on first populate */
+
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+
+    /*
+     * Register tl2 first so it's visited second (QLIST_INSERT_HEAD reverses
+     * registration order). This ensures tl1 receives populate before tl2
+     * fails.
+     */
+    ram_discard_manager_register_listener(rdm, &tl2.rdl, &section);
+    ram_discard_manager_register_listener(rdm, &tl1.rdl, &section);
+
+    /* Try to populate - should fail and roll back */
+    test_source_populate(src, 0, GRANULARITY_4K);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              0, GRANULARITY_4K);
+    g_assert_cmpint(ret, ==, -ENOMEM);
+
+    /* First listener should have received populate then discard (rollback) */
+    g_assert_cmpint(tl1.populate_count, ==, 1);
+    g_assert_cmpint(tl1.discard_count, ==, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl1.rdl);
+    ram_discard_manager_unregister_listener(rdm, &tl2.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Replay populated with two sources (intersection).
+ */
+static void test_replay_populated_intersection(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /*
+     * src1: blocks 0-7 populated
+     * src2: blocks 4-11 populated
+     * Intersection: blocks 4-7
+     */
+    test_source_populate(src1, 0, GRANULARITY_4K * 8);
+    test_source_populate(src2, GRANULARITY_4K * 4, GRANULARITY_4K * 8);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener - should only get notified about intersection */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Should have been notified about blocks 4-7 (intersection) */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_offset, ==, GRANULARITY_4K * 4);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 4);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Empty region (no sources).
+ */
+static void test_no_sources(void)
+{
+    test_setup();
+
+    /* No sources - should have no manager */
+    g_assert_null(memory_region_get_ram_discard_manager(test_mr));
+    g_assert_false(memory_region_has_ram_discard_manager(test_mr));
+
+    test_teardown();
+}
+
+static void test_redundant_discard(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Add sources */
+    ret = memory_region_add_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    ret = memory_region_add_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(TEST_REGION_SIZE);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Populate intersection (0-4K) in both sources */
+    test_source_populate(src1, 0, GRANULARITY_4K);
+    test_source_populate(src2, 0, GRANULARITY_4K);
+
+    /* Notify populate src1 - should trigger listener populate */
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src1),
+                                              0, GRANULARITY_4K);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl.populate_count, ==, 1);
+
+    /* Now Discard src1 -> Aggregate Discarded */
+    tl.discard_count = 0;
+    test_source_discard(src1, 0, GRANULARITY_4K);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src1), 0, GRANULARITY_4K);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+
+    /* Now Discard src2 -> Aggregate Discarded (Already Discarded!) */
+    /* Listener should NOT receive another discard notification for the same range. */
+    test_source_discard(src2, 0, GRANULARITY_4K);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src2), 0, GRANULARITY_4K);
+
+    g_assert_cmpint(tl.discard_count, ==, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+/*
+ * Test: Listener with partial section coverage.
+ * Listener should only receive notifications for its registered range.
+ */
+static void test_partial_listener_section(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Populate blocks 0-7 */
+    test_source_populate(src, 0, GRANULARITY_4K * 8);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener for only blocks 2-5 (not the full region) */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = GRANULARITY_4K * 2;
+    section.size = int128_make64(GRANULARITY_4K * 4);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Should be notified only about blocks 2-5 (intersection) */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_offset, ==, GRANULARITY_4K * 2);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 4);
+
+    /* Discard block 0 - outside listener's section, no notification */
+    tl.discard_count = 0;
+    test_source_discard(src, 0, GRANULARITY_4K);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src),
+                                       0, GRANULARITY_4K);
+    g_assert_cmpint(tl.discard_count, ==, 0);
+
+    /* Discard block 3 - inside listener's section */
+    test_source_discard(src, GRANULARITY_4K * 3, GRANULARITY_4K);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src),
+                                       GRANULARITY_4K * 3, GRANULARITY_4K);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+    g_assert_cmpuint(tl.last_discard_offset, ==, GRANULARITY_4K * 3);
+
+    /* Discard spanning boundary (blocks 5-6) - only block 5 in section */
+    tl.discard_count = 0;
+    test_source_discard(src, GRANULARITY_4K * 5, GRANULARITY_4K * 2);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src),
+                                       GRANULARITY_4K * 5, GRANULARITY_4K * 2);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+    g_assert_cmpuint(tl.last_discard_offset, ==, GRANULARITY_4K * 5);
+    g_assert_cmpuint(tl.last_discard_size, ==, GRANULARITY_4K);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Multiple listeners with different (non-overlapping) sections.
+ */
+static void test_multiple_listeners_different_sections(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section1, section2;
+    TestListener tl1 = { 0, }, tl2 = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Listener 1: blocks 0-3 */
+    test_listener_init(&tl1);
+    section1.mr = test_mr;
+    section1.offset_within_region = 0;
+    section1.size = int128_make64(GRANULARITY_4K * 4);
+    ram_discard_manager_register_listener(rdm, &tl1.rdl, &section1);
+
+    /* Listener 2: blocks 8-11 */
+    test_listener_init(&tl2);
+    section2.mr = test_mr;
+    section2.offset_within_region = GRANULARITY_4K * 8;
+    section2.size = int128_make64(GRANULARITY_4K * 4);
+    ram_discard_manager_register_listener(rdm, &tl2.rdl, &section2);
+
+    /* Initially all discarded - no populate notifications */
+    g_assert_cmpint(tl1.populate_count, ==, 0);
+    g_assert_cmpint(tl2.populate_count, ==, 0);
+
+    /* Populate blocks 0-3 - only tl1 should be notified */
+    test_source_populate(src, 0, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              0, GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 1);
+    g_assert_cmpint(tl2.populate_count, ==, 0);
+
+    /* Populate blocks 8-11 - only tl2 should be notified */
+    test_source_populate(src, GRANULARITY_4K * 8, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              GRANULARITY_4K * 8,
+                                              GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 1);
+    g_assert_cmpint(tl2.populate_count, ==, 1);
+
+    /* Populate blocks 4-7 (gap) - neither listener should be notified */
+    test_source_populate(src, GRANULARITY_4K * 4, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              GRANULARITY_4K * 4,
+                                              GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 1);
+    g_assert_cmpint(tl2.populate_count, ==, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl2.rdl);
+    ram_discard_manager_unregister_listener(rdm, &tl1.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Multiple listeners with overlapping sections.
+ */
+static void test_overlapping_listener_sections(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section1, section2;
+    TestListener tl1 = { 0, }, tl2 = { 0, };
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Listener 1: blocks 0-7 */
+    test_listener_init(&tl1);
+    section1.mr = test_mr;
+    section1.offset_within_region = 0;
+    section1.size = int128_make64(GRANULARITY_4K * 8);
+    ram_discard_manager_register_listener(rdm, &tl1.rdl, &section1);
+
+    /* Listener 2: blocks 4-11 (overlaps with tl1 on blocks 4-7) */
+    test_listener_init(&tl2);
+    section2.mr = test_mr;
+    section2.offset_within_region = GRANULARITY_4K * 4;
+    section2.size = int128_make64(GRANULARITY_4K * 8);
+    ram_discard_manager_register_listener(rdm, &tl2.rdl, &section2);
+
+    /* Populate blocks 4-7 (overlap region) - both should be notified */
+    test_source_populate(src, GRANULARITY_4K * 4, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              GRANULARITY_4K * 4,
+                                              GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 1);
+    g_assert_cmpint(tl2.populate_count, ==, 1);
+
+    /* Populate blocks 0-3 - only tl1 */
+    test_source_populate(src, 0, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              0, GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 2);
+    g_assert_cmpint(tl2.populate_count, ==, 1);
+
+    /* Populate blocks 8-11 - only tl2 */
+    test_source_populate(src, GRANULARITY_4K * 8, GRANULARITY_4K * 4);
+    ret = ram_discard_manager_notify_populate(rdm, RAM_DISCARD_SOURCE(src),
+                                              GRANULARITY_4K * 8,
+                                              GRANULARITY_4K * 4);
+    g_assert_cmpint(ret, ==, 0);
+    g_assert_cmpint(tl1.populate_count, ==, 2);
+    g_assert_cmpint(tl2.populate_count, ==, 2);
+
+    ram_discard_manager_unregister_listener(rdm, &tl2.rdl);
+    ram_discard_manager_unregister_listener(rdm, &tl1.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+/*
+ * Test: Listener at exact memory region boundaries.
+ */
+static void test_boundary_section(void)
+{
+    TestRamDiscardSource *src;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    TestListener tl = { 0, };
+    uint64_t last_offset;
+    int ret;
+
+    test_setup();
+
+    src = test_source_new(test_mr, GRANULARITY_4K);
+
+    /* Populate last 4 blocks of the region */
+    last_offset = TEST_REGION_SIZE - GRANULARITY_4K * 4;
+    test_source_populate(src, last_offset, GRANULARITY_4K * 4);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src));
+    g_assert_cmpint(ret, ==, 0);
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    /* Register listener for exactly the last 4 blocks */
+    test_listener_init(&tl);
+    section.mr = test_mr;
+    section.offset_within_region = last_offset;
+    section.size = int128_make64(GRANULARITY_4K * 4);
+    ram_discard_manager_register_listener(rdm, &tl.rdl, &section);
+
+    /* Should receive notification for the populated range */
+    g_assert_cmpint(tl.populate_count, ==, 1);
+    g_assert_cmpuint(tl.last_populate_offset, ==, last_offset);
+    g_assert_cmpuint(tl.last_populate_size, ==, GRANULARITY_4K * 4);
+
+    /* Discard exactly at boundary */
+    tl.discard_count = 0;
+    test_source_discard(src, last_offset, GRANULARITY_4K * 4);
+    ram_discard_manager_notify_discard(rdm, RAM_DISCARD_SOURCE(src),
+                                       last_offset, GRANULARITY_4K * 4);
+    g_assert_cmpint(tl.discard_count, ==, 1);
+
+    ram_discard_manager_unregister_listener(rdm, &tl.rdl);
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src));
+    test_source_free(src);
+    test_teardown();
+}
+
+static int count_discarded_blocks(const MemoryRegionSection *section,
+                                  void *opaque)
+{
+    int *count = opaque;
+    *count += int128_get64(section->size) / GRANULARITY_4K;
+    return 0;
+}
+
+/*
+ * Test: replay_discarded with two sources (union semantics).
+ */
+static void test_replay_discarded(void)
+{
+    TestRamDiscardSource *src1, *src2;
+    RamDiscardManager *rdm;
+    MemoryRegionSection section;
+    int count = 0;
+    int ret;
+
+    test_setup();
+
+    src1 = test_source_new(test_mr, GRANULARITY_4K);
+    src2 = test_source_new(test_mr, GRANULARITY_4K);
+
+    /*
+     * src1: blocks 0-3 populated, rest discarded
+     * src2: blocks 2-5 populated, rest discarded
+     * Aggregated populated: blocks 2-3 (intersection)
+     * Aggregated discarded: blocks 0-1, 4-5, 6+ (union of discarded)
+     */
+    test_source_populate(src1, 0, GRANULARITY_4K * 4);
+    test_source_populate(src2, GRANULARITY_4K * 2, GRANULARITY_4K * 4);
+
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src1));
+    g_assert_cmpint(ret, ==, 0);
+    ret = memory_region_add_ram_discard_source(test_mr,
+                                               RAM_DISCARD_SOURCE(src2));
+    g_assert_cmpint(ret, ==, 0);
+
+    rdm = memory_region_get_ram_discard_manager(test_mr);
+
+    section.mr = test_mr;
+    section.offset_within_region = 0;
+    section.size = int128_make64(GRANULARITY_4K * 8);
+
+    /* Count discarded blocks */
+    ret = ram_discard_manager_replay_discarded(rdm, &section,
+                                               count_discarded_blocks, &count);
+
+    g_assert_cmpint(ret, ==, 0);
+    /* Discarded: blocks 0-1 (2), blocks 4-5 (2), blocks 6-7 (2) = 6 blocks */
+    g_assert_cmpint(count, ==, 6);
+
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src2));
+    memory_region_del_ram_discard_source(test_mr, RAM_DISCARD_SOURCE(src1));
+
+    test_source_free(src2);
+    test_source_free(src1);
+    test_teardown();
+}
+
+int main(int argc, char **argv)
+{
+    g_test_init(&argc, &argv, NULL);
+
+    module_call_init(MODULE_INIT_QOM);
+    type_register_static(&test_rds_info);
+
+    g_test_add_func("/ram-discard-manager/single-source/basic",
+                    test_single_source_basic);
+    g_test_add_func("/ram-discard-manager/single-source/listener",
+                    test_single_source_listener);
+    g_test_add_func("/ram-discard-manager/two-sources/same-granularity",
+                    test_two_sources_same_granularity);
+    g_test_add_func("/ram-discard-manager/two-sources/different-granularity",
+                    test_two_sources_different_granularity);
+    g_test_add_func("/ram-discard-manager/two-sources/notification",
+                    test_two_sources_notification);
+    g_test_add_func("/ram-discard-manager/dynamic/add-source-with-listener",
+                    test_add_source_with_listener);
+    g_test_add_func("/ram-discard-manager/dynamic/remove-source-with-listener",
+                    test_remove_source_with_listener);
+    g_test_add_func("/ram-discard-manager/dynamic/readd-source-with-listener",
+                    test_readd_source_with_listener);
+    g_test_add_func("/ram-discard-manager/edge/duplicate-source",
+                    test_duplicate_source);
+    g_test_add_func("/ram-discard-manager/edge/populate-rollback",
+                    test_populate_rollback);
+    g_test_add_func("/ram-discard-manager/edge/replay-intersection",
+                    test_replay_populated_intersection);
+    g_test_add_func("/ram-discard-manager/edge/no-sources",
+                    test_no_sources);
+    g_test_add_func("/ram-discard-manager/multi-source/redundant-discard",
+                    test_redundant_discard);
+    g_test_add_func("/ram-discard-manager/listener/partial-section",
+                    test_partial_listener_section);
+    g_test_add_func("/ram-discard-manager/listener/multiple-different",
+                    test_multiple_listeners_different_sections);
+    g_test_add_func("/ram-discard-manager/listener/overlapping",
+                    test_overlapping_listener_sections);
+    g_test_add_func("/ram-discard-manager/edge/boundary-section",
+                    test_boundary_section);
+    g_test_add_func("/ram-discard-manager/multi-source/replay-discarded",
+                    test_replay_discarded);
+
+    return g_test_run();
+}
diff --git a/tests/unit/meson.build b/tests/unit/meson.build
index 01cc540a45..5ba6b1a230 100644
--- a/tests/unit/meson.build
+++ b/tests/unit/meson.build
@@ -138,7 +138,13 @@ if have_system
     'test-bufferiszero': [],
     'test-smp-parse': [qom, meson.project_source_root() / 'hw/core/machine-smp.c'],
     'test-vmstate': [migration, io],
-    'test-yank': ['socket-helpers.c', qom, io, chardev]
+    'test-yank': ['socket-helpers.c', qom, io, chardev],
+    'test-ram-discard-manager': [
+      'test-ram-discard-manager.c',
+      'test-ram-discard-manager-stubs.c',
+      meson.project_source_root() / 'system/ram-discard-manager.c',
+      genh, qemuutil, qom
+    ],
   }
   if config_host_data.get('CONFIG_INOTIFY1')
     tests += {'test-util-filemonitor': []}
-- 
2.54.0