KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-ocfs2 b/Documentation/ABI/testing/sysfs-ocfs2
new file mode 100644
index 000000000..494d7c1ac
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-ocfs2
@@ -0,0 +1,89 @@
+What:		/sys/fs/ocfs2/
+Date:		April 2008
+Contact:	ocfs2-devel@lists.linux.dev
+Description:
+		The /sys/fs/ocfs2 directory contains knobs used by the
+		ocfs2-tools to interact with the filesystem.
+
+What:		/sys/fs/ocfs2/max_locking_protocol
+Date:		April 2008
+Contact:	ocfs2-devel@lists.linux.dev
+Description:
+		The /sys/fs/ocfs2/max_locking_protocol file displays version
+		of ocfs2 locking supported by the filesystem.  This version
+		covers how ocfs2 uses distributed locking between cluster
+		nodes.
+
+		The protocol version has a major and minor number.  Two
+		cluster nodes can interoperate if they have an identical
+		major number and an overlapping minor number - thus,
+		a node with version 1.10 can interoperate with a node
+		sporting version 1.8, as long as both use the 1.8 protocol.
+
+		Reading from this file returns a single line, the major
+		number and minor number joined by a period, eg "1.10".
+
+		This file is read-only.  The value is compiled into the
+		driver.
+
+What:		/sys/fs/ocfs2/loaded_cluster_plugins
+Date:		April 2008
+Contact:	ocfs2-devel@lists.linux.dev
+Description:
+		The /sys/fs/ocfs2/loaded_cluster_plugins file describes
+		the available plugins to support ocfs2 cluster operation.
+		A cluster plugin is required to use ocfs2 in a cluster.
+		There are currently two available plugins:
+
+		* 'o2cb' - The classic o2cb cluster stack that ocfs2 has
+			used since its inception.
+		* 'user' - A plugin supporting userspace cluster software
+			in conjunction with fs/dlm.
+
+		Reading from this file returns the names of all loaded
+		plugins, one per line.
+
+		This file is read-only.  Its contents may change as
+		plugins are loaded or removed.
+
+What:		/sys/fs/ocfs2/active_cluster_plugin
+Date:		April 2008
+Contact:	ocfs2-devel@lists.linux.dev
+Description:
+		The /sys/fs/ocfs2/active_cluster_plugin displays which
+		cluster plugin is currently in use by the filesystem.
+		The active plugin will appear in the loaded_cluster_plugins
+		file as well.  Only one plugin can be used at a time.
+
+		Reading from this file returns the name of the active plugin
+		on a single line.
+
+		This file is read-only.  Which plugin is active depends on
+		the cluster stack in use.  The contents may change
+		when all filesystems are unmounted and the cluster stack
+		is changed.
+
+What:		/sys/fs/ocfs2/cluster_stack
+Date:		April 2008
+Contact:	ocfs2-devel@lists.linux.dev
+Description:
+		The /sys/fs/ocfs2/cluster_stack file contains the name
+		of current ocfs2 cluster stack.  This value is set by
+		userspace tools when bringing the cluster stack online.
+
+		Cluster stack names are 4 characters in length.
+
+		When the 'o2cb' cluster stack is used, the 'o2cb' cluster
+		plugin is active.  All other cluster stacks use the 'user'
+		cluster plugin.
+
+		Reading from this file returns the name of the current
+		cluster stack on a single line.
+
+		Writing a new stack name to this file changes the current
+		cluster stack unless there are mounted ocfs2 filesystems.
+		If there are mounted filesystems, attempts to change the
+		stack return an error.
+
+Users:
+	ocfs2-tools <ocfs2-tools-devel@lists.linux.dev>