madvise() not triggering page discard with MMU-notifiers

[Anthony Liguori <aliguori@us.ibm.com>]

[-- Attachment #1: Type: text/plain, Size: 450 bytes --]

Attached is an updated migration patch.  It does not appear, however, 
that madvise() is triggering discarding of pages even with an 
MMU-notifier enabled kernel.  I take it that this is because we're still 
holding a reference count to the page when it is in the shadow page 
table?  Any ETA on when this will change?

N.B. the virtio_balloon driver is broken in Linus' tree.  Sending patch 
for that following this one.

Regards,

Anthony Liguori


[-- Attachment #2: virtio-balloon-driver.patch --]
[-- Type: text/x-patch, Size: 11826 bytes --]

diff --git a/libkvm/libkvm.c b/libkvm/libkvm.c
index 5edfad7..ebee5b8 100644
--- a/libkvm/libkvm.c
+++ b/libkvm/libkvm.c
@@ -1053,6 +1053,15 @@ int kvm_pit_in_kernel(kvm_context_t kvm)
 	return kvm->pit_in_kernel;
 }
 
+int kvm_has_mmu_notifiers(kvm_context_t kvm)
+{
+        int r = 0;
+#ifdef KVM_CAP_SYNC_MMU
+        r = ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_CAP_SYNC_MMU);
+#endif
+        return r;
+}
+
 int kvm_init_coalesced_mmio(kvm_context_t kvm)
 {
 	int r = 0;
diff --git a/libkvm/libkvm.h b/libkvm/libkvm.h
index 9f06fcc..fb51ee1 100644
--- a/libkvm/libkvm.h
+++ b/libkvm/libkvm.h
@@ -528,6 +528,8 @@ int kvm_dirty_pages_log_reset(kvm_context_t kvm);
  */
 int kvm_irqchip_in_kernel(kvm_context_t kvm);
 
+int kvm_has_mmu_notifiers(kvm_context_t kvm);
+
 #ifdef KVM_CAP_IRQCHIP
 /*!
  * \brief Dump in kernel IRQCHIP contents
diff --git a/qemu/Makefile.target b/qemu/Makefile.target
index a86464f..cd985f6 100644
--- a/qemu/Makefile.target
+++ b/qemu/Makefile.target
@@ -598,7 +598,7 @@ OBJS += rtl8139.o
 OBJS += e1000.o
 
 # virtio devices
-OBJS += virtio.o virtio-net.o virtio-blk.o
+OBJS += virtio.o virtio-net.o virtio-blk.o virtio-balloon.o
 
 OBJS += device-hotplug.o
 
diff --git a/qemu/balloon.h b/qemu/balloon.h
new file mode 100644
index 0000000..60b4a5d
--- /dev/null
+++ b/qemu/balloon.h
@@ -0,0 +1,27 @@
+/*
+ * Balloon
+ *
+ * Copyright IBM, Corp. 2008
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef _QEMU_BALLOON_H
+#define _QEMU_BALLOON_H
+
+#include "cpu-defs.h"
+
+typedef ram_addr_t (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
+
+void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque);
+
+void qemu_balloon(ram_addr_t target);
+
+ram_addr_t qemu_balloon_status(void);
+
+#endif
diff --git a/qemu/hw/pc.c b/qemu/hw/pc.c
index 3a8269b..b19e558 100644
--- a/qemu/hw/pc.c
+++ b/qemu/hw/pc.c
@@ -1161,6 +1161,9 @@ static void pc_init1(ram_addr_t ram_size, int vga_ram_size,
 
 	extboot_init(info->bdrv, 1);
     }
+
+    if (pci_enabled)
+        virtio_balloon_init(pci_bus);
 }
 
 static void pc_init_pci(ram_addr_t ram_size, int vga_ram_size,
diff --git a/qemu/hw/pc.h b/qemu/hw/pc.h
index c284bf1..5b68d69 100644
--- a/qemu/hw/pc.h
+++ b/qemu/hw/pc.h
@@ -164,4 +164,7 @@ void *virtio_blk_init(PCIBus *bus, uint16_t vendor, uint16_t device,
 
 void extboot_init(BlockDriverState *bs, int cmd);
 
+/* virtio-balloon.h */
+void *virtio_balloon_init(PCIBus *bus);
+
 #endif
diff --git a/qemu/hw/virtio-balloon.c b/qemu/hw/virtio-balloon.c
new file mode 100644
index 0000000..457b88f
--- /dev/null
+++ b/qemu/hw/virtio-balloon.c
@@ -0,0 +1,194 @@
+/*
+ * Virtio Block Device
+ *
+ * Copyright IBM, Corp. 2008
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "virtio.h"
+#include "pc.h"
+#include "sysemu.h"
+#include "cpu.h"
+#include "balloon.h"
+#include "virtio-balloon.h"
+#include "qemu-kvm.h"
+
+#if defined(__linux__)
+#include <sys/mman.h>
+#endif
+
+typedef struct VirtIOBalloon
+{
+    VirtIODevice vdev;
+    VirtQueue *ivq, *dvq;
+    uint32_t num_pages;
+    uint32_t actual;
+} VirtIOBalloon;
+
+static VirtIOBalloon *to_virtio_balloon(VirtIODevice *vdev)
+{
+    return (VirtIOBalloon *)vdev;
+}
+
+static void balloon_page(void *addr, int deflate)
+{
+#if defined(__linux__)
+    if (!kvm_enabled() || !qemu_kvm_has_mmu_notifiers())
+        madvise(addr, TARGET_PAGE_SIZE,
+                deflate ? MADV_WILLNEED : MADV_DONTNEED);
+#endif
+}
+
+/* FIXME: once we do a virtio refactoring, this will get subsumed into common
+ * code */
+static size_t memcpy_from_iovector(void *data, size_t offset, size_t size,
+                                   struct iovec *iov, int iovlen)
+{
+    int i;
+    uint8_t *ptr = data;
+    size_t iov_off = 0;
+    size_t data_off = 0;
+
+    for (i = 0; i < iovlen && size; i++) {
+        if (offset < (iov_off + iov[i].iov_len)) {
+            size_t len = MIN((iov_off + iov[i].iov_len) - offset , size);
+
+            memcpy(ptr + data_off, iov[i].iov_base + (offset - iov_off), len);
+
+            data_off += len;
+            offset += len;
+            size -= len;
+        }
+
+        iov_off += iov[i].iov_len;
+    }
+
+    return data_off;
+}
+
+static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = to_virtio_balloon(vdev);
+    VirtQueueElement elem;
+
+    while (virtqueue_pop(vq, &elem)) {
+	size_t offset = 0;
+	uint32_t pfn;
+
+	while (memcpy_from_iovector(&pfn, offset, 4, 
+                                    elem.out_sg, elem.out_num) == 4) {
+	    ram_addr_t pa;
+	    ram_addr_t addr;
+
+	    pa = (ram_addr_t)ldl_p(&pfn) << TARGET_PAGE_BITS;
+	    offset += 4;
+
+	    addr = cpu_get_physical_page_desc(pa);
+	    if ((addr & ~TARGET_PAGE_MASK) != IO_MEM_RAM)
+		continue;
+
+	    balloon_page(phys_ram_base + addr, !!(vq == s->dvq));
+	}
+
+	virtqueue_push(vq, &elem, offset);
+	virtio_notify(vdev, vq);
+    }
+}
+
+static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
+{
+    VirtIOBalloon *dev = to_virtio_balloon(vdev);
+    struct virtio_balloon_config config;
+
+    config.num_pages = cpu_to_le32(dev->num_pages);
+    config.actual = cpu_to_le32(dev->actual);
+
+    memcpy(config_data, &config, 8);
+}
+
+static void virtio_balloon_set_config(VirtIODevice *vdev,
+				      const uint8_t *config_data)
+{
+    VirtIOBalloon *dev = to_virtio_balloon(vdev);
+    struct virtio_balloon_config config;
+    memcpy(&config, config_data, 8);
+    dev->actual = config.actual;
+}
+
+static uint32_t virtio_balloon_get_features(VirtIODevice *vdev)
+{
+    return 0;
+}
+
+static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
+{
+    VirtIOBalloon *dev = opaque;
+
+    if (target > ram_size)
+	target = ram_size;
+
+    if (target) {
+	dev->num_pages = (ram_size - target) >> TARGET_PAGE_BITS;
+	virtio_notify_config(&dev->vdev);
+    }
+
+    return ram_size - (dev->actual << TARGET_PAGE_BITS);
+}
+
+static void virtio_balloon_save(QEMUFile *f, void *opaque)
+{
+    VirtIOBalloon *s = opaque;
+
+    virtio_save(&s->vdev, f);
+
+    qemu_put_be32(f, s->num_pages);
+    qemu_put_be32(f, s->actual);
+}
+
+static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
+{
+    VirtIOBalloon *s = opaque;
+
+    if (version_id != 1)
+        return -EINVAL;
+
+    virtio_load(&s->vdev, f);
+
+    s->num_pages = qemu_get_be32(f);
+    s->actual = qemu_get_be32(f);
+
+    return 0;
+}
+
+void *virtio_balloon_init(PCIBus *bus)
+{
+    VirtIOBalloon *s;
+
+    s = (VirtIOBalloon *)virtio_init_pci(bus, "virtio-balloon",
+					 6900, 0x1002,
+					 0, VIRTIO_ID_BALLOON,
+					 0x05, 0x00, 0x00,
+					 8, sizeof(VirtIOBalloon));
+    if (s == NULL)
+        return NULL;
+
+    s->vdev.get_config = virtio_balloon_get_config;
+    s->vdev.set_config = virtio_balloon_set_config;
+    s->vdev.get_features = virtio_balloon_get_features;
+
+    s->ivq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
+    s->dvq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
+
+    qemu_add_balloon_handler(virtio_balloon_to_target, s);
+
+    register_savevm("virtio-balloon", -1, 1, virtio_balloon_save, virtio_balloon_load, s);
+
+    return &s->vdev;
+}
diff --git a/qemu/hw/virtio-balloon.h b/qemu/hw/virtio-balloon.h
new file mode 100644
index 0000000..27d6985
--- /dev/null
+++ b/qemu/hw/virtio-balloon.h
@@ -0,0 +1,34 @@
+/*
+ * Virtio Support
+ *
+ * Copyright IBM, Corp. 2007-2008
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *  Rusty Russell     <rusty@rustcorp.com.au>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef _QEMU_VIRTIO_BALLOON_H
+#define _QEMU_VIRTIO_BALLOON_H
+
+/* from Linux's linux/virtio_balloon.h */
+
+/* The ID for virtio_balloon */
+#define VIRTIO_ID_BALLOON	5
+
+/* The feature bitmap for virtio balloon */
+#define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
+
+struct virtio_balloon_config
+{
+    /* Number of pages host wants Guest to give up. */
+    uint32_t num_pages;
+    /* Number of pages we've actually got in balloon. */
+    uint32_t actual;
+};
+
+#endif
diff --git a/qemu/monitor.c b/qemu/monitor.c
index 4acf346..b8c4fde 100644
--- a/qemu/monitor.c
+++ b/qemu/monitor.c
@@ -35,6 +35,7 @@
 #include "audio/audio.h"
 #include "disas.h"
 #include "migration.h"
+#include "balloon.h"
 #include <dirent.h>
 #include "qemu-timer.h"
 
@@ -1399,6 +1400,25 @@ static void do_inject_nmi(int cpu_index)
 }
 #endif
 
+static void do_balloon(int value)
+{
+    ram_addr_t target = value;
+    qemu_balloon(target << 20);
+}
+
+static void do_info_balloon(void)
+{
+    ram_addr_t actual;
+
+    actual = qemu_balloon_status();
+    if (kvm_enabled() && !qemu_kvm_has_mmu_notifiers())
+        term_printf("Using KVM without MMU-notifiers, ballooning disabled\n");
+    else if (actual == 0)
+	term_printf("Ballooning not activated in VM\n");
+    else
+	term_printf("balloon: actual=%d\n", (int)(actual >> 20));
+}
+
 static term_cmd_t term_cmds[] = {
     { "help|?", "s?", do_help,
       "[cmd]", "show the help" },
@@ -1494,6 +1514,8 @@ static term_cmd_t term_cmds[] = {
     { "pci_add", "iss", device_hot_add, "bus nic|storage [[vlan=n][,macaddr=addr][,model=type]] [file=file][,if=type][,bus=nr]...", "hot-add PCI device" },
     { "pci_del", "ii", device_hot_remove, "bus slot-number", "hot remove PCI device" },
 #endif
+    { "balloon", "i", do_balloon,
+      "target", "request VM to change it's memory allocation (in MB)" },
     { NULL, NULL, },
 };
 
@@ -1558,6 +1580,8 @@ static term_cmd_t info_cmds[] = {
 #endif
     { "migration", "", do_info_migration,
       "", "show migration information" },
+    { "balloon", "", do_info_balloon,
+      "", "show balloon information" },
     { NULL, NULL, },
 };
 
diff --git a/qemu/qemu-kvm.h b/qemu/qemu-kvm.h
index 7e28428..088bae3 100644
--- a/qemu/qemu-kvm.h
+++ b/qemu/qemu-kvm.h
@@ -110,10 +110,12 @@ extern kvm_context_t kvm_context;
 #define kvm_enabled() (kvm_allowed)
 #define qemu_kvm_irqchip_in_kernel() kvm_irqchip_in_kernel(kvm_context)
 #define qemu_kvm_pit_in_kernel() kvm_pit_in_kernel(kvm_context)
+#define qemu_kvm_has_mmu_notifiers() kvm_has_mmu_notifiers(kvm_context)
 #else
 #define kvm_enabled() (0)
 #define qemu_kvm_irqchip_in_kernel() (0)
 #define qemu_kvm_pit_in_kernel() (0)
+#define qemu_kvm_has_mmu_notifiers() (0)
 #endif
 
 void kvm_mutex_unlock(void);
diff --git a/qemu/vl.c b/qemu/vl.c
index 2dc1311..ec89921 100644
--- a/qemu/vl.c
+++ b/qemu/vl.c
@@ -38,6 +38,7 @@
 #include "block.h"
 #include "audio/audio.h"
 #include "migration.h"
+#include "balloon.h"
 #include "qemu-kvm.h"
 
 #include <unistd.h>
@@ -530,6 +531,31 @@ void hw_error(const char *fmt, ...)
     va_end(ap);
     abort();
 }
+ 
+/***************/
+/* ballooning */
+
+static QEMUBalloonEvent *qemu_balloon_event;
+void *qemu_balloon_event_opaque;
+
+void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque)
+{
+    qemu_balloon_event = func;
+    qemu_balloon_event_opaque = opaque;
+}
+
+void qemu_balloon(ram_addr_t target)
+{
+    if (qemu_balloon_event)
+	qemu_balloon_event(qemu_balloon_event_opaque, target);
+}
+
+ram_addr_t qemu_balloon_status(void)
+{
+    if (qemu_balloon_event)
+	return qemu_balloon_event(qemu_balloon_event_opaque, 0);
+    return 0;
+}
 
 /***********************************************************/
 /* keyboard/mouse */