[PATCH v5 0/6] elf: THP-aware load segment alignment

[caiyinyu]

LGTM

在 2026/3/6 下午9:40, WANG Rui 写道:
> Changes since [v4]:
>    * Merge malloc-hugepages into hugepages.
>    * Limit the glibc.elf.hugetlb tunable maximum value to 1.
>
> Changes since [v3]:
>    * Rebased on current master.
>    * Resolved conflicts with recently merged changes.
>    * No functional changes intended.
>
> Changes since [v2]:
>    * Refactor THP detection into a new generic hugepages abstraction,
>      moving helpers out of malloc-hugepages.
>    * Add a new tunable, `glibc.elf.hugetlb`, to control THP-aware ELF
>      segment alignment.
>    * Move the Linux implementation of `_dl_map_segment_align` to
>      sysdeps/unix/sysv/linux/, making it generic for Linux (including
>      32-bit) and avoiding wordsize-64-specific overrides.
>    * Use `static inline` instead of `static __always_inline`.
>
> Changes since [v1]:
>    * Fix CI build failure (-Wunused-function).
>
> This patch series introduces a small extension point in the ELF loader to allow
> architecture-specific adjustment of load segment alignment, and uses it to
> improve Transparent Huge Page (THP) usage on Linux.
>
> Patch 1 moves Transparent Huge Page helpers into a new generic hugepages
> abstraction, so THP mode detection and default huge page size probing can be
> shared between malloc and the dynamic loader. There is no functional change.
>
> Patch 2 removes a redundant declaration of `_dl_map_segments` from
> dl-load.h, avoiding `-Wunused-function` build failures and keeping the
> prototype colocated with its definition.
>
> Patch 3 adds a new helper, `_dl_map_segment_align`, which is called when
> determining the maximum alignment for ELF load segments. The generic
> implementation is a no-op and preserves existing behavior.
>
> Patch 4 introduces a new tunable, `glibc.elf.hugetlb`, which controls
> THP-aware alignment of ELF loadable segments. By default, the value is 0
> and existing behavior is preserved.
>
> Patch 5 provides a Linux implementation of `_dl_map_segment_align` that
> opportunistically aligns large, suitably aligned, non-writable `PT_LOAD`
> segments to the system’s default THP page size when THP is configured to
> be used unconditionally and the tunable is enabled.
>
> Patch 6 enables this behavior by default on LoongArch64 Linux and defines
> the default THP page size (32MB), matching the architecture’s PMD huge page
> geometry.
>
> [v4]: https://sourceware.org/pipermail/libc-alpha/2026-March/175644.html
> [v3]: https://sourceware.org/pipermail/libc-alpha/2026-February/175464.html
> [v2]: https://sourceware.org/pipermail/libc-alpha/2026-February/175394.html
> [v1]: https://sourceware.org/pipermail/libc-alpha/2026-February/175359.html
>
> WANG Rui (6):
>    hugepages: Move THP helpers to generic hugepages abstraction
>    elf: Remove redundant _dl_map_segments declaration from dl-load.h
>    elf: Introduce _dl_map_segment_align hook for segment alignment tuning
>    tunables: Add glibc.elf.hugetlb tunable for THP-aware segment
>      alignment
>    elf: Align large load segments to PMD huge page size for THP
>    loongarch: Enable THP-aligned load segments by default on 64-bit
>
>   elf/dl-load.c                                 |  4 ++
>   elf/dl-load.h                                 |  5 +-
>   elf/dl-tunables.list                          |  8 +++
>   malloc/arena.c                                | 12 ++---
>   malloc/malloc-internal.h                      |  2 +-
>   malloc/malloc.c                               | 17 +++---
>   manual/tunables.texi                          | 24 +++++++++
>   sysdeps/generic/Makefile                      |  4 +-
>   sysdeps/generic/dl-map-segment-align.h        | 26 +++++++++
>   .../{malloc-hugepages.c => hugepages.c}       | 13 +++--
>   .../{malloc-hugepages.h => hugepages.h}       | 28 +++++-----
>   sysdeps/unix/sysv/linux/Makefile              |  1 +
>   .../{malloc-hugepages.h => hugepages.h}       |  4 +-
>   .../unix/sysv/linux/dl-map-segment-align.c    | 54 +++++++++++++++++++
>   .../unix/sysv/linux/dl-map-segment-align.h    | 27 ++++++++++
>   .../linux/{malloc-hugepages.c => hugepages.c} | 33 ++++++------
>   .../unix/sysv/linux/loongarch/cpu-features.c  |  6 +++
>   .../loongarch/lp64/dl-map-segment-align.h     | 22 ++++++++
>   18 files changed, 231 insertions(+), 59 deletions(-)
>   create mode 100644 sysdeps/generic/dl-map-segment-align.h
>   rename sysdeps/generic/{malloc-hugepages.c => hugepages.c} (76%)
>   rename sysdeps/generic/{malloc-hugepages.h => hugepages.h} (68%)
>   rename sysdeps/unix/sysv/linux/aarch64/{malloc-hugepages.h => hugepages.h} (91%)
>   create mode 100644 sysdeps/unix/sysv/linux/dl-map-segment-align.c
>   create mode 100644 sysdeps/unix/sysv/linux/dl-map-segment-align.h
>   rename sysdeps/unix/sysv/linux/{malloc-hugepages.c => hugepages.c} (89%)
>   create mode 100644 sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
>