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, 60 insertions, 0 deletions

diff --git a/scripts/stackdelta b/scripts/stackdelta
new file mode 100755
index 000000000..44d2dfd62
--- /dev/null
+++ b/scripts/stackdelta
@@ -0,0 +1,60 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+
+# Read two files produced by the stackusage script, and show the
+# delta between them.
+#
+# Currently, only shows changes for functions listed in both files. We
+# could add an option to show also functions which have vanished or
+# appeared (which would often be due to gcc making other inlining
+# decisions).
+#
+# Another possible option would be a minimum absolute value for the
+# delta.
+#
+# A third possibility is for sorting by delta, but that can be
+# achieved by piping to sort -k5,5g.
+
+sub read_stack_usage_file {
+    my %su;
+    my $f = shift;
+    open(my $fh, '<', $f)
+	or die "cannot open $f: $!";
+    while (<$fh>) {
+	chomp;
+	my ($file, $func, $size, $type) = split;
+	# Old versions of gcc (at least 4.7) have an annoying quirk in
+	# that a (static) function whose name has been changed into
+	# for example ext4_find_unwritten_pgoff.isra.11 will show up
+	# in the .su file with a name of just "11". Since such a
+	# numeric suffix is likely to change across different
+	# commits/compilers/.configs or whatever else we're trying to
+	# tweak, we can't really track those functions, so we just
+	# silently skip them.
+	#
+	# Newer gcc (at least 5.0) report the full name, so again,
+	# since the suffix is likely to change, we strip it.
+	next if $func =~ m/^[0-9]+$/;
+	$func =~ s/\..*$//;
+	# Line numbers are likely to change; strip those.
+	$file =~ s/:[0-9]+$//;
+	$su{"${file}\t${func}"} = {size => $size, type => $type};
+    }
+    close($fh);
+    return \%su;
+}
+
+@ARGV == 2
+    or die "usage: $0 <old> <new>";
+
+my $old = read_stack_usage_file($ARGV[0]);
+my $new = read_stack_usage_file($ARGV[1]);
+my @common = sort grep {exists $new->{$_}} keys %$old;
+for (@common) {
+    my $x = $old->{$_}{size};
+    my $y = $new->{$_}{size};
+    my $delta = $y - $x;
+    if ($delta) {
+	printf "%s\t%d\t%d\t%+d\n", $_, $x, $y, $delta;
+    }
+}