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, 217 insertions, 0 deletions

diff --git a/lib/region_alloc_benchmark.c b/lib/region_alloc_benchmark.c
new file mode 100644
index 000000000..e88b4cf55
--- /dev/null
+++ b/lib/region_alloc_benchmark.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Benchmark bitmap, IDA and Maple Tree allocation of variable-sized regions. */
+
+#include <linux/bitmap.h>
+#include <linux/idr.h>
+#include <linux/kernel.h>
+#include <linux/maple_tree.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/xarray.h>
+
+#define REGION_MAX_SIZE	32
+
+static unsigned long *bitmap __initdata;
+/* One more request guarantees that even an all-ones trace reaches ENOSPC. */
+static u8 *reg_sz __initdata;
+static unsigned long *reg_idx __initdata;
+static unsigned long capacities[64] = { 1000000, 100000, 10000, 1000, 100, 10 };
+static unsigned int cap_cnt = 6;
+
+module_param_array(capacities, ulong, &cap_cnt, 0400);
+MODULE_PARM_DESC(capacities, "Region capacities to benchmark");
+
+static unsigned long __init benchmark_bitmap(unsigned long cap)
+{
+	unsigned long cnt, idx;
+	ktime_t alloc_time, free_time;
+	size_t sz;
+
+	bitmap_zero(bitmap, cap);
+	alloc_time = ktime_get();
+	for (cnt = 0; cnt <= cap; cnt++) {
+		idx = bitmap_find_next_zero_area(bitmap, cap, 0, reg_sz[cnt], 0);
+		if (idx >= cap)
+			break;
+
+		reg_idx[cnt] = idx;
+		bitmap_set(bitmap, idx, reg_sz[cnt]);
+	}
+	alloc_time = ktime_get() - alloc_time;
+
+	idx = cnt;
+
+	free_time = ktime_get();
+	while (idx--)
+		bitmap_clear(bitmap, reg_idx[idx], reg_sz[idx]);
+	free_time = ktime_get() - free_time;
+
+	WARN_ON(!bitmap_empty(bitmap, cap));
+
+	sz = BITS_TO_LONGS(cap) * sizeof(unsigned long);
+	pr_err("Bitmap  %12llu  %12llu  %8lu  %8lu  %10zu\n",
+	       alloc_time, free_time, cnt, cap, sz);
+
+	return cnt;
+}
+
+static size_t __init ida_size(unsigned long nr_ids)
+{
+	unsigned long entries = DIV_ROUND_UP(nr_ids, IDA_BITMAP_BITS);
+	unsigned long bitmaps = nr_ids / IDA_BITMAP_BITS;
+	unsigned long nodes = 0;
+
+	if (nr_ids % IDA_BITMAP_BITS > BITS_PER_XA_VALUE)
+		bitmaps++;
+
+	while (entries > 1) {
+		entries = DIV_ROUND_UP(entries, XA_CHUNK_SIZE);
+		nodes += entries;
+	}
+
+	return sizeof(struct ida) +
+		bitmaps * sizeof(struct ida_bitmap) +
+		nodes   * sizeof(struct xa_node);
+}
+
+static unsigned long __init benchmark_ida(unsigned long cap)
+{
+	struct ida ida = IDA_INIT(ida);
+	unsigned long cnt, idx, off, nr_ids = 0;
+	ktime_t alloc_time, free_time;
+	int id = -ENOSPC;
+
+	alloc_time = ktime_get();
+	for (cnt = 0; cnt <= cap; cnt++) {
+		for (off = 0; off < reg_sz[cnt]; off++) {
+			id = ida_alloc_max(&ida, cap - 1, GFP_KERNEL);
+			if (id < 0)
+				break;
+
+			if (!off)
+				reg_idx[cnt] = id;
+		}
+		if (id < 0) {
+			while (off--)
+				ida_free(&ida, reg_idx[cnt] + off);
+			break;
+		}
+		WARN_ON(id != reg_idx[cnt] + reg_sz[cnt] - 1);
+		nr_ids += reg_sz[cnt];
+	}
+	alloc_time = ktime_get() - alloc_time;
+
+	WARN_ON(id != -ENOSPC);
+
+	idx = cnt;
+
+	free_time = ktime_get();
+	while (idx--) {
+		for (off = 0; off < reg_sz[idx]; off++)
+			ida_free(&ida, reg_idx[idx] + off);
+	}
+	free_time = ktime_get() - free_time;
+
+	WARN_ON(!ida_is_empty(&ida));
+
+	pr_err("IDA     %12llu  %12llu  %8lu  %8lu  %10zu\n",
+	       alloc_time, free_time, cnt, cap, ida_size(nr_ids));
+
+	ida_destroy(&ida);
+	return cnt;
+}
+
+static unsigned long __init benchmark_maple_tree(unsigned long cap)
+{
+	struct maple_tree mt = MTREE_INIT(mt, MT_FLAGS_ALLOC_RANGE);
+	unsigned long cnt, idx;
+	ktime_t alloc_time, free_time;
+	size_t sz;
+	int ret;
+
+	alloc_time = ktime_get();
+	for (cnt = 0; cnt <= cap; cnt++) {
+		ret = mtree_alloc_range(&mt, &idx, xa_mk_value(cnt + 1),
+					reg_sz[cnt], 0, cap - 1, GFP_KERNEL);
+		if (ret)
+			break;
+
+		reg_idx[cnt] = idx;
+	}
+	alloc_time = ktime_get() - alloc_time;
+
+	WARN_ON(ret != -EBUSY);
+
+	idx = cnt;
+
+	free_time = ktime_get();
+	while (idx--)
+		mtree_erase(&mt, reg_idx[idx]);
+	free_time = ktime_get() - free_time;
+
+	WARN_ON(!mtree_empty(&mt));
+
+	/* Minimum storage assuming fully occupied allocation-range leaf nodes. */
+	sz = sizeof(mt) + DIV_ROUND_UP(cnt, MAPLE_ARANGE64_SLOTS) * sizeof(struct maple_node);
+	pr_err("Maple   %12llu  %12llu  %8lu  %8lu  %10zu\n",
+	       alloc_time, free_time, cnt, cap, sz);
+
+	mtree_destroy(&mt);
+	return cnt;
+}
+
+static int __init region_alloc_benchmark(void)
+{
+	unsigned long bitmap_count, ida_count, maple_count;
+	unsigned long i, max_cap = 0;
+	int ret = -ENOMEM;
+
+	for (i = 0; i < cap_cnt; i++) {
+		if (capacities[i] == 0) {
+			pr_err("capacity must be nonzero\n");
+			return -EINVAL;
+		}
+		max_cap = max(max_cap, capacities[i]);
+	}
+
+	bitmap = kvmalloc_array(BITS_TO_LONGS(max_cap), sizeof(*bitmap), GFP_KERNEL);
+	reg_sz = kvmalloc_array(max_cap + 1, sizeof(*reg_sz), GFP_KERNEL);
+	reg_idx = kvmalloc_array(max_cap, sizeof(*reg_idx), GFP_KERNEL);
+	if (!bitmap || !reg_sz || !reg_idx)
+		goto out;
+
+	pr_err("\nStart testing bitmap vs IDA vs Maple Tree region allocation\n");
+	pr_err("memory: bitmap is exact; IDA and Maple Tree are lower bounds\n");
+	pr_err("Type      alloc (ns)     free (ns)   regions  capacity  memory (B)\n");
+
+	for (i = 0; i < cap_cnt; i++) {
+		unsigned long idx, max_size;
+
+		max_size = min(REGION_MAX_SIZE, capacities[i] / 10) ? : 1;
+		for (idx = 0; idx <= capacities[i]; idx++)
+			reg_sz[idx] = get_random_u32_below(max_size) + 1;
+
+		bitmap_count = benchmark_bitmap(capacities[i]);
+		maple_count  = benchmark_maple_tree(capacities[i]);
+		ida_count    = benchmark_ida(capacities[i]);
+
+		WARN_ON(bitmap_count != ida_count);
+		WARN_ON(bitmap_count != maple_count);
+	}
+
+	/* Return an error so the benchmark can run repeatedly without rmmod. */
+	pr_info("Region allocation benchmark complete\n");
+	ret = -EAGAIN;
+out:
+	kvfree(reg_idx);
+	kvfree(reg_sz);
+	kvfree(bitmap);
+	return ret;
+}
+module_init(region_alloc_benchmark);
+
+MODULE_AUTHOR("Yury Norov <ynorov@nvidia.com>");
+MODULE_DESCRIPTION("Benchmark bitmap, IDA and Maple Tree region allocation");
+MODULE_LICENSE("GPL");