[PATCH v8 0/6] elf: THP-aware load segment alignment

[H.J. Lu]

On Tue, Apr 7, 2026 at 7:32 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Sun, Apr 5, 2026 at 11:54 AM WANG Rui <wangrui@loongson.cn> wrote:
> >
> > OK for commit?
> >
> > Changes since [v7]:
> >   * Rename tunable glibc.elf.hugetlb to glibc.elf.thp.
> >   * Rebase on current master.
> >
> > Changes since [v6]:
> >   * Move MAX_THP_PAGESIZE to hugepages.
> >   * Skip THP mode probing when DL_MAP_DEFAULT_THP_PAGESIZE is non-zero.
> >
> > Changes since [v5]:
> >   * No functional changes.
> >   * Add benchmark results to the commit message.
> >
> > 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.
> >
> > [v7]: https://sourceware.org/pipermail/libc-alpha/2026-March/175776.html
> > [v6]: https://sourceware.org/pipermail/libc-alpha/2026-March/175737.html
> > [v5]: https://sourceware.org/pipermail/libc-alpha/2026-March/175694.html
> > [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.thp 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.c                             |  7 +--
> >  elf/dl-tunables.list                          |  8 +++
> >  malloc/malloc-internal.h                      |  2 +-
> >  malloc/malloc.c                               | 27 +++++-----
> >  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}       | 32 ++++++-----
> >  sysdeps/unix/sysv/linux/Makefile              |  1 +
> >  .../{malloc-hugepages.h => hugepages.h}       |  4 +-
> >  .../unix/sysv/linux/dl-map-segment-align.c    | 53 +++++++++++++++++++
> >  .../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, 237 insertions(+), 61 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
> >
> > --
> > 2.53.0
> >
>
> Please add some tests for this feature.
>

I opened:

https://sourceware.org/bugzilla/show_bug.cgi?id=34056

for GNU_PROPERTY_1_NEEDED_TRANSPARENT_HUGEPAGE.

-- 
H.J.