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From 5643e64ad775e2a14c76faa867ad698c5e1fe9c7 Mon Sep 17 00:00:00 2001
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From: David Gibson <dgibson@redhat.com>
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Date: Thu, 16 Nov 2017 03:07:32 +0100
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Subject: [PATCH 28/30] memory: Share special empty FlatView
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RH-Author: David Gibson <dgibson@redhat.com>
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Message-id: <20171116030732.8560-23-dgibson@redhat.com>
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Patchwork-id: 77711
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O-Subject: [PATCH 22/22] memory: Share special empty FlatView
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Bugzilla: 1481593
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com>
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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From: Alexey Kardashevskiy <aik@ozlabs.ru>
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This shares an cached empty FlatView among address spaces. The empty
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FV is used every time when a root MR renders into a FV without memory
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sections which happens when MR or its children are not enabled or
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zero-sized. The empty_view is not NULL to keep the rest of memory
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API intact; it also has a dispatch tree for the same reason.
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On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves
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the amount of FlatView's in use (557 -> 260) and dispatch tables
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(~800000 -> ~370000). In an unrelated experiment with 112 non-virtio
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devices on x86 ("-M pc"), only 4 FlatViews are alive, and about ~2000
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are created at startup.
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Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
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Message-Id: <20170921085110.25598-16-aik@ozlabs.ru>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit 092aa2fc65b7a35121616aad8f39d47b8f921618)
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Signed-off-by: David Gibson <dgibson@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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memory.c | 18 ++++++++++++++++--
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1 file changed, 16 insertions(+), 2 deletions(-)
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diff --git a/memory.c b/memory.c
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index 38eabe7..a1f1e68 100644
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--- a/memory.c
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+++ b/memory.c
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@@ -317,6 +317,7 @@ static void flatview_unref(FlatView *view)
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{
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if (atomic_fetch_dec(&view->ref) == 1) {
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trace_flatview_destroy_rcu(view, view->root);
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+ assert(view->root);
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call_rcu(view, flatview_destroy, rcu);
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}
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}
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@@ -760,16 +761,19 @@ static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr)
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}
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}
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}
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+ if (found == 0) {
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+ return NULL;
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+ }
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if (next) {
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mr = next;
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continue;
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}
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}
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- break;
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+ return mr;
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}
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- return mr;
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+ return NULL;
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}
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/* Render a memory topology into a list of disjoint absolute ranges. */
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@@ -965,12 +969,22 @@ static void address_space_update_topology_pass(AddressSpace *as,
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static void flatviews_init(void)
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{
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+ static FlatView *empty_view;
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+
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if (flat_views) {
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return;
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}
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flat_views = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL,
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(GDestroyNotify) flatview_unref);
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+ if (!empty_view) {
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+ empty_view = generate_memory_topology(NULL);
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+ /* We keep it alive forever in the global variable. */
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+ flatview_ref(empty_view);
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+ } else {
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+ g_hash_table_replace(flat_views, NULL, empty_view);
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+ flatview_ref(empty_view);
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+ }
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}
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static void flatviews_reset(void)
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--
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1.8.3.1
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