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X-Received-From: 2a00:1450:400c:c09::242 Subject: [Qemu-devel] [PULL 24/32] memory: Share special empty FlatView X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexey Kardashevskiy Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZohoMail: RDKM_2 RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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) =3D=3D 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 =3D=3D 0) { + return NULL; + } if (next) { mr =3D next; continue; } } =20 - break; + return mr; } =20 - return mr; + return NULL; } =20 /* Render a memory topology into a list of disjoint absolute ranges. */ @@ -966,12 +970,22 @@ static void address_space_update_topology_pass(Addres= sSpace *as, =20 static void flatviews_init(void) { + static FlatView *empty_view; + if (flat_views) { return; } =20 flat_views =3D g_hash_table_new_full(g_direct_hash, g_direct_equal, NU= LL, (GDestroyNotify) flatview_unref); + if (!empty_view) { + empty_view =3D 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); + } } =20 static void flatviews_reset(void) --=20 1.8.3.1