From: Jianfeng Tan <jianfeng.tan@intel.com>
Date: Wed, 28 Mar 2018 06:56:07 +0000 (+0000)
Subject: vhost: avoid populate guest memory
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=768274ebbd5e532134420146cc26b1ff4b607740;p=dpdk.git

vhost: avoid populate guest memory

It's not necessary to populate guest memory from vhost side unless
zerocopy is enabled or users want better performance.

Update the doc for guest memory requirement clarification.

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index 18227b6a34..f474736093 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -214,6 +214,27 @@ the vhost device from the data plane.
 
 When the socket connection is closed, vhost will destroy the device.
 
+Guest memory requirement
+------------------------
+
+* Memory pre-allocation
+
+  For non-zerocopy, guest memory pre-allocation is not a must. This can help
+  save of memory. If users really want the guest memory to be pre-allocated
+  (e.g., for performance reason), we can add option ``-mem-prealloc`` when
+  starting QEMU. Or, we can lock all memory at vhost side which will force
+  memory to be allocated when mmap at vhost side; option --mlockall in
+  ovs-dpdk is an example in hand.
+
+  For zerocopy, we force the VM memory to be pre-allocated at vhost lib when
+  mapping the guest memory; and also we need to lock the memory to prevent
+  pages being swapped out to disk.
+
+* Memory sharing
+
+  Make sure ``share=on`` QEMU option is given. vhost-user will not work with
+  a QEMU version without shared memory mapping.
+
 Vhost supported vSwitch reference
 ---------------------------------
 
diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index a4bdc6a45a..da161a9a91 100644
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -175,15 +175,6 @@ Common Issues
   The command above indicates how many hugepages are free to support QEMU's
   allocation request.
 
-* vhost-user will not work with QEMU without the ``-mem-prealloc`` option
-
-  The current implementation works properly only when the guest memory is
-  pre-allocated.
-
-* vhost-user will not work with a QEMU version without shared memory mapping:
-
-  Make sure ``share=on`` QEMU option is given.
-
 * Failed to build DPDK in VM
 
   Make sure "-cpu host" QEMU option is given.
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 08956dc3e9..66e1b82a50 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -684,6 +684,7 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
 	uint64_t mmap_offset;
 	uint64_t alignment;
 	uint32_t i;
+	int populate;
 	int fd;
 
 	if (memory.nregions > VHOST_MEMORY_MAX_NREGIONS) {
@@ -770,8 +771,9 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
 		}
 		mmap_size = RTE_ALIGN_CEIL(mmap_size, alignment);
 
+		populate = (dev->dequeue_zero_copy) ? MAP_POPULATE : 0;
 		mmap_addr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
-				 MAP_SHARED | MAP_POPULATE, fd, 0);
+				 MAP_SHARED | populate, fd, 0);
 
 		if (mmap_addr == MAP_FAILED) {
 			RTE_LOG(ERR, VHOST_CONFIG,