[Qemu-devel] [PATCH for-2.5 4/4] vhost: simplify/speedify vhost_dev_unassign_memory()

[Igor Mammedov <imammedo@redhat.com>]

beside reducing code size 2x times, it also makes
function faster and easier to read.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/virtio/vhost.c | 111 ++++++++++++++++++------------------------------------
 1 file changed, 37 insertions(+), 74 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 5b8598b..e2585e3 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -160,91 +160,54 @@ static int memory_range_bsearch(const struct vhost_dev *dev,
     return start;
 }
 
-/* Assign/unassign. Keep an unsorted array of non-overlapping
- * memory regions in dev->mem. */
 static void vhost_dev_unassign_memory(struct vhost_dev *dev,
                                       uint64_t start_addr,
                                       uint64_t size)
 {
-    int from, to, n = dev->mem->nregions;
-    /* Track overlapping/split regions for sanity checking. */
-    int overlap_start = 0, overlap_end = 0, overlap_middle = 0, split = 0;
-
-    for (from = 0, to = 0; from < n; ++from, ++to) {
-        struct vhost_memory_region *reg = dev->mem->regions + to;
-        uint64_t reglast;
-        uint64_t memlast;
-        uint64_t change;
-
-        /* clone old region */
-        if (to != from) {
-            memcpy(reg, dev->mem->regions + from, sizeof *reg);
-        }
-
-        /* No overlap is simple */
-        if (!ranges_overlap(reg->guest_phys_addr, reg->memory_size,
-                            start_addr, size)) {
-            continue;
-        }
-
-        /* Split only happens if supplied region
-         * is in the middle of an existing one. Thus it can not
-         * overlap with any other existing region. */
-        assert(!split);
+    uint64_t reglast, memlast;
+    struct vhost_memory_region *reg;
+    int idx = memory_range_bsearch(dev, start_addr);
 
-        reglast = range_get_last(reg->guest_phys_addr, reg->memory_size);
-        memlast = range_get_last(start_addr, size);
+    if (idx == dev->mem->nregions) { /* not found any range */
+        return;
+    }
 
-        /* Remove whole region */
-        if (start_addr <= reg->guest_phys_addr && memlast >= reglast) {
-            --dev->mem->nregions;
-            --to;
-            ++overlap_middle;
-            continue;
-        }
+    reg = dev->mem->regions + idx;
+    reglast = range_get_last(reg->guest_phys_addr, reg->memory_size);
+    memlast = range_get_last(start_addr, size);
 
-        /* Shrink region */
-        if (memlast >= reglast) {
-            reg->memory_size = start_addr - reg->guest_phys_addr;
-            assert(reg->memory_size);
-            assert(!overlap_end);
-            ++overlap_end;
-            continue;
-        }
+    /* Remove whole region */
+    if (start_addr == reg->guest_phys_addr && memlast == reglast) {
+        memmove(reg, reg + 1, (dev->mem->nregions - idx - 1) *
+                               sizeof dev->mem->regions[0]);
+        dev->mem->nregions--;
+        return;
+    }
 
-        /* Shift region */
-        if (start_addr <= reg->guest_phys_addr) {
-            change = memlast + 1 - reg->guest_phys_addr;
-            reg->memory_size -= change;
-            reg->guest_phys_addr += change;
-            reg->userspace_addr += change;
-            assert(reg->memory_size);
-            assert(!overlap_start);
-            ++overlap_start;
-            continue;
-        }
+    /* Split region */
+    if (start_addr > reg->guest_phys_addr && memlast < reglast) {
+        memmove(reg + 1, reg, (dev->mem->nregions - idx) *
+                               sizeof dev->mem->regions[0]);
+        reg->guest_phys_addr = memlast + 1;
+        reg->memory_size = reglast - reg->guest_phys_addr + 1;
+        reg++;
+        reg->memory_size = start_addr - reg->guest_phys_addr;
+        dev->mem->nregions++;
+        return;
+    }
 
-        /* This only happens if supplied region
-         * is in the middle of an existing one. Thus it can not
-         * overlap with any other existing region. */
-        assert(!overlap_start);
-        assert(!overlap_end);
-        assert(!overlap_middle);
-        /* Split region: shrink first part, shift second part. */
-        memcpy(dev->mem->regions + n, reg, sizeof *reg);
+    /* Shrink region */
+    if (memlast == reglast) { /* shrink end side */
         reg->memory_size = start_addr - reg->guest_phys_addr;
-        assert(reg->memory_size);
-        change = memlast + 1 - reg->guest_phys_addr;
-        reg = dev->mem->regions + n;
-        reg->memory_size -= change;
-        assert(reg->memory_size);
-        reg->guest_phys_addr += change;
-        reg->userspace_addr += change;
-        /* Never add more than 1 region */
-        assert(dev->mem->nregions == n);
-        ++dev->mem->nregions;
-        ++split;
+        return;
+    } else if (start_addr == reg->guest_phys_addr) { /* shrink start side */
+        reg->guest_phys_addr = memlast + 1;
+        reg->memory_size = reglast - reg->guest_phys_addr + 1;
+        return;
     }
+    /* there shouldn't be any overlapped ranges by now */
+    assert(!ranges_overlap(reg->guest_phys_addr, reg->memory_size,
+                           start_addr, size));
 }
 
 /* Called after unassign, so no regions overlap the given range. */
-- 
1.8.3.1