From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49094) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eMfCG-0000VJ-KZ for qemu-devel@nongnu.org; Wed, 06 Dec 2017 14:17:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eMfCD-0000Pm-Gm for qemu-devel@nongnu.org; Wed, 06 Dec 2017 14:17:32 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:47330 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eMfCD-0000Oy-BC for qemu-devel@nongnu.org; Wed, 06 Dec 2017 14:17:29 -0500 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vB6JE3jg015520 for ; Wed, 6 Dec 2017 14:17:28 -0500 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0b-001b2d01.pphosted.com with ESMTP id 2epn0ac18d-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 06 Dec 2017 14:17:28 -0500 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 6 Dec 2017 14:17:28 -0500 From: Michael Roth Date: Wed, 6 Dec 2017 13:16:17 -0600 In-Reply-To: <20171206191648.18208-1-mdroth@linux.vnet.ibm.com> References: <20171206191648.18208-1-mdroth@linux.vnet.ibm.com> Message-Id: <20171206191648.18208-25-mdroth@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH 24/55] memory: Share special empty FlatView List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Alexey Kardashevskiy , Paolo Bonzini 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 (cherry picked from commit 092aa2fc65b7a35121616aad8f39d47b8f921618) Signed-off-by: Michael Roth --- memory.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/memory.c b/memory.c index 231bb78fa7..d90853855b 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); } } @@ -760,16 +761,19 @@ 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. */ @@ -965,12 +969,22 @@ 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) -- 2.11.0