[PATCH] qemu-options.hx: Update descriptions of memory options for NUMA node

[Yohei Kojima]

This commit adds the following description:
1. `memdev` option is recommended over `mem` option (see [1,2])
2. users must specify memory for all NUMA nodes (see [2])

This commit also separates descriptions for `mem` and `memdev` into two
paragraphs. The old doc describes legacy `mem` option first, and it was
a bit confusing.

Related documantations:
[1] https://wiki.qemu.org/ChangeLog/5.1#Incompatible_changes
[2] https://www.qemu.org/docs/master/about/removed-features.html

Signed-off-by: Yohei Kojima <y-koj@outlook.jp>
---
 qemu-options.hx | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 59bdf67a2c..174f0d0c2d 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -405,15 +405,22 @@ SRST
         -numa node,nodeid=0 -numa node,nodeid=1 \
         -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1
 
-    Legacy '\ ``mem``\ ' assigns a given RAM amount to a node (not supported
-    for 5.1 and newer machine types). '\ ``memdev``\ ' assigns RAM from
-    a given memory backend device to a node. If '\ ``mem``\ ' and
-    '\ ``memdev``\ ' are omitted in all nodes, RAM is split equally between 
them.
-
-
-    '\ ``mem``\ ' and '\ ``memdev``\ ' are mutually exclusive.
-    Furthermore, if one node uses '\ ``memdev``\ ', all of them have to
-    use it.
+    '\ ``memdev``\ ' option assigns RAM from a given memory backend
+    device to a node. It is recommended to use '\ ``memdev``\ ' option
+    over legacy '\ ``mem``\ ' option. This is because '\ ``memdev``\ '
+    option provides better performance and more control over the
+    backend's RAM (e.g. '\ ``prealloc``\ ' parameter of
+    '\ ``-memory-backend-ram``\ ' allows memory preallocation).
+
+    For compatibility reasons, legacy '\ ``mem``\ ' option is
+    supported in 5.0 and older machine types. Note that '\ ``mem``\ '
+    and '\ ``memdev``\ ' are mutually exclusive. If one node uses
+    '\ ``memdev``\ ', the rest nodes have to use '\ ``memdev``\ '
+    option, and vice versa.
+
+    Users must specify memory for all NUMA nodes by '\ ``memdev``\ '
+    (or legacy '\ ``mem``\ ' if available). In QEMU 5.2, the support
+    for '\ ``-numa node``\ ' without memory specified was removed.
 
     '\ ``initiator``\ ' is an additional option that points to an
     initiator NUMA node that has best performance (the lowest latency or
-- 
2.39.2