[PATCH v8 6/6] loongarch: Enable THP-aligned load segments by default on 64-bit

[WANG Rui]

On LoongArch64 Linux, aligning ELF load segments to Transparent Huge Page
(THP) boundaries provides consistent performance benefits for large
binaries by reducing TLB pressure and improving instruction fetch
efficiency.

Enable THP-based load segment alignment by default on LoongArch64 by
setting `glibc.elf.thp=1` during startup. Define the default THP
page size for load segment alignment on LoongArch64 as 32MB.

This allows the dynamic loader to apply THP-friendly alignment without
requiring the `glibc.elf.thp` tunable to be explicitly set.

Benchmarks

Machine: Loongson 3A6000 (LoongArch64)
Kernel: 6.18.13
  CONFIG_READ_ONLY_THP_FOR_FS=y
  CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y

Workload 1: building Cargo 1.93.0
Rustc: nightly-2026-02-26

                Without patch        With patch
instructions    3,690,358,948,176    3,690,301,774,568
cpu-cycles      4,233,025,766,760    4,035,866,635,741
itlb-misses     9,708,829,532        2,700,014,717
time elapsed    302.40 s             289.68 s

Instructions remain essentially unchanged. iTLB misses drop by about
72%, reducing CPU cycles by about 4.7% and wall time by about 4.2%.

Workload 2: building Linux kernel v7.0-rc1
LLVM: 21.1.8

                Without patch        With patch
instructions    14,163,739,876,387   14,169,418,598,675
cpu-cycles      19,231,890,317,741   16,851,494,928,181
itlb-misses     91,142,010,440       90,779,245
time elapsed    1022.09 s            893.22 s

Instructions remain roughly the same. iTLB misses drop from about 91B
to about 90M (roughly 99.9% reduction), reducing CPU cycles by about
12% and wall time by about 12.6%.

Reviewed-by: caiyinyu <caiyinyu@loongson.cn>
Signed-off-by: WANG Rui <wangrui@loongson.cn>
---
 .../unix/sysv/linux/loongarch/cpu-features.c  |  6 +++++
 .../loongarch/lp64/dl-map-segment-align.h     | 22 +++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h

diff --git a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
index 0c125e64e2b..7ed54ff53e7 100644
--- a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
@@ -27,4 +27,10 @@ init_cpu_features (struct cpu_features *cpu_features)
   GLRO(dl_larch_cpu_features).hwcap = GLRO(dl_hwcap);
   TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *,
 	       TUNABLE_CALLBACK (set_hwcaps));
+
+#ifdef __LP64__
+  /* Enable THP-based load segment alignment by default on LoongArch64. */
+  if (!TUNABLE_IS_INITIALIZED (glibc, elf, thp))
+    TUNABLE_SET (glibc, elf, thp, 1);
+#endif
 }
diff --git a/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h b/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
new file mode 100644
index 00000000000..c51ee4ac47e
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
@@ -0,0 +1,22 @@
+/* _dl_map_segment_align.  LoongArch64 Linux version.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#define DL_MAP_DEFAULT_THP_PAGESIZE (32 * 1024 * 1024)
+
+#include_next <dl-map-segment-align.h>
-- 
2.53.0