[PATCH] elf: Add transparent huge page marker and _dl_map_segment_adjust
H.J. Lu
hjl.tools@gmail.com
Wed Apr 8 07:47:25 GMT 2026
On Wed, Apr 8, 2026 at 10:07 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> 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.
>
Here is a patch on top of yours to implement
GNU_PROPERTY_1_NEEDED_TRANSPARENT_HUGEPAGE and
add _dl_map_segment_adjust.
--
H.J.
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