diff mbox

[02/10] memory: add support getting and using a dirty bitmap copy.

Message ID 20170404102315.24923-3-kraxel@redhat.com
State New, archived
Headers show

Commit Message

Gerd Hoffmann April 4, 2017, 10:23 a.m. UTC
This patch adds support for getting and using a local copy of the dirty
bitmap.

memory_region_copy_and_clear_dirty() will create a copy of the dirty
bitmap for the specified range, clear the dirty bitmap and return the
copy.  The returned bitmap can be a bit larger than requested, the range
is expanded so the code can copy unsigned longs from the bitmap and
avoid atomic bit update operations.

memory_region_copy_get_dirty() will return the dirty status of pages,
pretty much like memory_region_get_dirty(), but using the copy returned
by memory_region_copy_and_clear_dirty().

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 include/exec/memory.h   | 47 +++++++++++++++++++++++++++++++
 include/exec/ram_addr.h |  7 +++++
 include/qemu/typedefs.h |  1 +
 exec.c                  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++
 memory.c                | 17 +++++++++++
 5 files changed, 147 insertions(+)

Comments

Paolo Bonzini April 4, 2017, 10:29 a.m. UTC | #1
On 04/04/2017 12:23, Gerd Hoffmann wrote:
> 
> memory_region_copy_and_clear_dirty() will create a copy of the dirty
> bitmap for the specified range, clear the dirty bitmap and return the
> copy.  The returned bitmap can be a bit larger than requested, the range
> is expanded so the code can copy unsigned longs from the bitmap and
> avoid atomic bit update operations.
> 
> memory_region_copy_get_dirty() will return the dirty status of pages,
> pretty much like memory_region_get_dirty(), but using the copy returned
> by memory_region_copy_and_clear_dirty().

Old names in the commit message, otherwise looks good.

This will also help KVM by the way, because there are changes in the
pipeline to limit the amount of work done by log_sync and process dirty
pages periodically in the VCPU thread.

Paolo
diff mbox

Patch

diff --git a/include/exec/memory.h b/include/exec/memory.h
index e39256a..2d82983 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -871,6 +871,53 @@  void memory_region_set_dirty(MemoryRegion *mr, hwaddr addr,
  */
 bool memory_region_test_and_clear_dirty(MemoryRegion *mr, hwaddr addr,
                                         hwaddr size, unsigned client);
+
+/**
+ * memory_region_snapshot_and_clear_dirty: Get a snapshot of the dirty
+ *                                         bitmap and clear it.
+ *
+ * Creates a snapshot of the dirty bitmap, clears the dirty bitmap and
+ * returns the snapshot.  The snapshot can then be used to query dirty
+ * status, using memory_region_snapshot_get_dirty.  Unlike
+ * memory_region_test_and_clear_dirty this allows to query the same
+ * page multiple times, which is especially useful for display updates
+ * where the scanlines often are not page aligned.
+ *
+ * The dirty bitmap region which gets copyed into the snapshot (and
+ * cleared afterwards) can be larger than requested.  The boundaries
+ * are rounded up/down so complete bitmap longs (covering 64 pages on
+ * 64bit hosts) can be copied over into the bitmap snapshot.  Which
+ * isn't a problem for display updates as the extra pages are outside
+ * the visible area, and in case the visible area changes a full
+ * display redraw is due anyway.  Should other use cases for this
+ * function emerge we might have to revisit this implementation
+ * detail.
+ *
+ * Use g_free to release DirtyBitmapSnapshot.
+ *
+ * @mr: the memory region being queried.
+ * @addr: the address (relative to the start of the region) being queried.
+ * @size: the size of the range being queried.
+ * @client: the user of the logging information; typically %DIRTY_MEMORY_VGA.
+ */
+DirtyBitmapSnapshot *memory_region_snapshot_and_clear_dirty(MemoryRegion *mr,
+                                                            hwaddr addr,
+                                                            hwaddr size,
+                                                            unsigned client);
+
+/**
+ * memory_region_snapshot_get_dirty: Check whether a range of bytes is dirty
+ *                                   in the specified dirty bitmap snapshot.
+ *
+ * @mr: the memory region being queried.
+ * @snap: the dirty bitmap snapshot
+ * @addr: the address (relative to the start of the region) being queried.
+ * @size: the size of the range being queried.
+ */
+bool memory_region_snapshot_get_dirty(MemoryRegion *mr,
+                                      DirtyBitmapSnapshot *snap,
+                                      hwaddr addr, hwaddr size);
+
 /**
  * memory_region_sync_dirty_bitmap: Synchronize a region's dirty bitmap with
  *                                  any external TLBs (e.g. kvm)
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index b05dc84..2b63d7f 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -343,6 +343,13 @@  bool cpu_physical_memory_test_and_clear_dirty(ram_addr_t start,
                                               ram_addr_t length,
                                               unsigned client);
 
+DirtyBitmapSnapshot *cpu_physical_memory_snapshot_and_clear_dirty
+    (ram_addr_t start, ram_addr_t length, unsigned client);
+
+bool cpu_physical_memory_snapshot_get_dirty(DirtyBitmapSnapshot *snap,
+                                            ram_addr_t start,
+                                            ram_addr_t length);
+
 static inline void cpu_physical_memory_clear_dirty_range(ram_addr_t start,
                                                          ram_addr_t length)
 {
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index e95f28c..f08d327 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -23,6 +23,7 @@  typedef struct CPUAddressSpace CPUAddressSpace;
 typedef struct CPUState CPUState;
 typedef struct DeviceListener DeviceListener;
 typedef struct DeviceState DeviceState;
+typedef struct DirtyBitmapSnapshot DirtyBitmapSnapshot;
 typedef struct DisplayChangeListener DisplayChangeListener;
 typedef struct DisplayState DisplayState;
 typedef struct DisplaySurface DisplaySurface;
diff --git a/exec.c b/exec.c
index e57a8a2..0b654b2 100644
--- a/exec.c
+++ b/exec.c
@@ -223,6 +223,12 @@  struct CPUAddressSpace {
     MemoryListener tcg_as_listener;
 };
 
+struct DirtyBitmapSnapshot {
+    ram_addr_t start;
+    ram_addr_t end;
+    unsigned long dirty[];
+};
+
 #endif
 
 #if !defined(CONFIG_USER_ONLY)
@@ -1061,6 +1067,75 @@  bool cpu_physical_memory_test_and_clear_dirty(ram_addr_t start,
     return dirty;
 }
 
+DirtyBitmapSnapshot *cpu_physical_memory_snapshot_and_clear_dirty
+     (ram_addr_t start, ram_addr_t length, unsigned client)
+{
+    DirtyMemoryBlocks *blocks;
+    unsigned long align = 1UL << (TARGET_PAGE_BITS + BITS_PER_LEVEL);
+    ram_addr_t first = QEMU_ALIGN_DOWN(start, align);
+    ram_addr_t last  = QEMU_ALIGN_UP(start + length, align);
+    DirtyBitmapSnapshot *snap;
+    unsigned long page, end, dest;
+
+    snap = g_malloc0(sizeof(*snap) +
+                     ((last - first) >> (TARGET_PAGE_BITS + 3)));
+    snap->start = first;
+    snap->end   = last;
+
+    page = first >> TARGET_PAGE_BITS;
+    end  = last  >> TARGET_PAGE_BITS;
+    dest = 0;
+
+    rcu_read_lock();
+
+    blocks = atomic_rcu_read(&ram_list.dirty_memory[client]);
+
+    while (page < end) {
+        unsigned long idx = page / DIRTY_MEMORY_BLOCK_SIZE;
+        unsigned long offset = page % DIRTY_MEMORY_BLOCK_SIZE;
+        unsigned long num = MIN(end - page, DIRTY_MEMORY_BLOCK_SIZE - offset);
+
+        assert(QEMU_IS_ALIGNED(offset, (1 << BITS_PER_LEVEL)));
+        assert(QEMU_IS_ALIGNED(num,    (1 << BITS_PER_LEVEL)));
+        offset >>= BITS_PER_LEVEL;
+
+        bitmap_copy_and_clear_atomic(snap->dirty + dest,
+                                     blocks->blocks[idx] + offset,
+                                     num);
+        page += num;
+        dest += num >> BITS_PER_LEVEL;
+    }
+
+    rcu_read_unlock();
+
+    if (tcg_enabled()) {
+        tlb_reset_dirty_range_all(start, length);
+    }
+
+    return snap;
+}
+
+bool cpu_physical_memory_snapshot_get_dirty(DirtyBitmapSnapshot *snap,
+                                            ram_addr_t start,
+                                            ram_addr_t length)
+{
+    unsigned long page, end;
+
+    assert(start >= snap->start);
+    assert(start + length <= snap->end);
+
+    end = TARGET_PAGE_ALIGN(start + length - snap->start) >> TARGET_PAGE_BITS;
+    page = (start - snap->start) >> TARGET_PAGE_BITS;
+
+    while (page < end) {
+        if (test_bit(page, snap->dirty)) {
+            return true;
+        }
+        page++;
+    }
+    return false;
+}
+
 /* Called from RCU critical section */
 hwaddr memory_region_section_get_iotlb(CPUState *cpu,
                                        MemoryRegionSection *section,
diff --git a/memory.c b/memory.c
index 4c95aaf..8a06485 100644
--- a/memory.c
+++ b/memory.c
@@ -1716,6 +1716,23 @@  bool memory_region_test_and_clear_dirty(MemoryRegion *mr, hwaddr addr,
                 memory_region_get_ram_addr(mr) + addr, size, client);
 }
 
+DirtyBitmapSnapshot *memory_region_snapshot_and_clear_dirty(MemoryRegion *mr,
+                                                            hwaddr addr,
+                                                            hwaddr size,
+                                                            unsigned client)
+{
+    assert(mr->ram_block);
+    return cpu_physical_memory_snapshot_and_clear_dirty(
+                memory_region_get_ram_addr(mr) + addr, size, client);
+}
+
+bool memory_region_snapshot_get_dirty(MemoryRegion *mr, DirtyBitmapSnapshot *snap,
+                                      hwaddr addr, hwaddr size)
+{
+    assert(mr->ram_block);
+    return cpu_physical_memory_snapshot_get_dirty(snap,
+                memory_region_get_ram_addr(mr) + addr, size);
+}
 
 void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
 {