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, 16 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-swap b/Documentation/ABI/testing/sysfs-kernel-mm-swap
new file mode 100644
index 000000000..94672016c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-swap
@@ -0,0 +1,16 @@
+What:		/sys/kernel/mm/swap/
+Date:		August 2017
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Interface for swapping
+
+What:		/sys/kernel/mm/swap/vma_ra_enabled
+Date:		August 2017
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Enable/disable VMA based swap readahead.
+
+		If set to true, the VMA based swap readahead algorithm
+		will be used for swappable anonymous pages mapped in a
+		VMA, and the global swap readahead algorithm will be
+		still used for tmpfs etc. other users.  If set to
+		false, the global swap readahead algorithm will be
+		used for all swappable pages.