From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37477) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dvAiY-0004vM-5k for qemu-devel@nongnu.org; Thu, 21 Sep 2017 19:17:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dvAiX-0004VB-5r for qemu-devel@nongnu.org; Thu, 21 Sep 2017 19:17:14 -0400 Received: from mail-wm0-x242.google.com ([2a00:1450:400c:c09::242]:33272) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1dvAiW-0004U6-V3 for qemu-devel@nongnu.org; Thu, 21 Sep 2017 19:17:13 -0400 Received: by mail-wm0-x242.google.com with SMTP id m127so6458962wmm.0 for ; Thu, 21 Sep 2017 16:17:12 -0700 (PDT) Sender: Paolo Bonzini From: Paolo Bonzini Date: Fri, 22 Sep 2017 01:16:32 +0200 Message-Id: <1506035800-30509-25-git-send-email-pbonzini@redhat.com> In-Reply-To: <1506035800-30509-1-git-send-email-pbonzini@redhat.com> References: <1506035800-30509-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PULL 24/32] memory: Share special empty FlatView List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Alexey Kardashevskiy From: Alexey Kardashevskiy This shares an cached empty FlatView among address spaces. The empty FV is used every time when a root MR renders into a FV without memory sections which happens when MR or its children are not enabled or zero-sized. The empty_view is not NULL to keep the rest of memory API intact; it also has a dispatch tree for the same reason. On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves the amount of FlatView's in use (557 -> 260) and dispatch tables (~800000 -> ~370000). In an unrelated experiment with 112 non-virtio devices on x86 ("-M pc"), only 4 FlatViews are alive, and about ~2000 are created at startup. Signed-off-by: Alexey Kardashevskiy Message-Id: <20170921085110.25598-16-aik@ozlabs.ru> Signed-off-by: Paolo Bonzini --- memory.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/memory.c b/memory.c index 15b1bd7..5e6351a 100644 --- a/memory.c +++ b/memory.c @@ -317,6 +317,7 @@ static void flatview_unref(FlatView *view) { if (atomic_fetch_dec(&view->ref) == 1) { trace_flatview_destroy_rcu(view, view->root); + assert(view->root); call_rcu(view, flatview_destroy, rcu); } } @@ -761,16 +762,19 @@ static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr) } } } + if (found == 0) { + return NULL; + } if (next) { mr = next; continue; } } - break; + return mr; } - return mr; + return NULL; } /* Render a memory topology into a list of disjoint absolute ranges. */ @@ -966,12 +970,22 @@ static void address_space_update_topology_pass(AddressSpace *as, static void flatviews_init(void) { + static FlatView *empty_view; + if (flat_views) { return; } flat_views = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL, (GDestroyNotify) flatview_unref); + if (!empty_view) { + empty_view = generate_memory_topology(NULL); + /* We keep it alive forever in the global variable. */ + flatview_ref(empty_view); + } else { + g_hash_table_replace(flat_views, NULL, empty_view); + flatview_ref(empty_view); + } } static void flatviews_reset(void) -- 1.8.3.1