From e673ba9af9bf8fd8e0f44025ac738b8285b3ed27 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 21 Sep 2017 12:28:16 +0200
Subject: [PATCH] memory: seek FlatView sharing candidates among children
subregions
A container can be used instead of an alias to allow switching between
multiple subregions. In this case we cannot directly share the
subregions (since they only belong to a single parent), but if the
subregions are aliases we can in turn walk those.
This is not enough to remove all source of quadratic FlatView creation,
but it enables sharing of the PCI bus master FlatViews (and their
AddressSpaceDispatch structures) across all PCI devices. For 112
virtio-net-pci devices, boot time is reduced from 25 to 10 seconds and
memory consumption from 1.4 to 1 G.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
memory.c | 40 ++++++++++++++++++++++++++++++++++------
1 file changed, 34 insertions(+), 6 deletions(-)
diff --git a/memory.c b/memory.c
index 68cdf8bad0c..15b1bd7d897 100644
--- a/memory.c
+++ b/memory.c
@@ -734,12 +734,40 @@ static void render_memory_region(FlatView *view,
static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr)
{
- while (mr->alias && !mr->alias_offset &&
- int128_ge(mr->size, mr->alias->size)) {
- /* The alias is included in its entirety. Use it as
- * the "real" root, so that we can share more FlatViews.
- */
- mr = mr->alias;
+ while (mr->enabled) {
+ if (mr->alias) {
+ if (!mr->alias_offset && int128_ge(mr->size, mr->alias->size)) {
+ /* The alias is included in its entirety. Use it as
+ * the "real" root, so that we can share more FlatViews.
+ */
+ mr = mr->alias;
+ continue;
+ }
+ } else if (!mr->terminates) {
+ unsigned int found = 0;
+ MemoryRegion *child, *next = NULL;
+ QTAILQ_FOREACH(child, &mr->subregions, subregions_link) {
+ if (child->enabled) {
+ if (++found > 1) {
+ next = NULL;
+ break;
+ }
+ if (!child->addr && int128_ge(mr->size, child->size)) {
+ /* A child is included in its entirety. If it's the only
+ * enabled one, use it in the hope of finding an alias down the
+ * way. This will also let us share FlatViews.
+ */
+ next = child;
+ }
+ }
+ }
+ if (next) {
+ mr = next;
+ continue;
+ }
+ }
+
+ break;
}
return mr;
--
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