[Bug dynamic-link/34083] __get_thp_mode and __get_thp_size are called twice

https://sourceware.org/bugzilla/show_bug.cgi?id=34083

--- Comment #2 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <[email protected]>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ccd4cd5324caaaea1bb12bc8cef073170da51a19

commit ccd4cd5324caaaea1bb12bc8cef073170da51a19
Author: H.J. Lu <[email protected]>
Date:   Sat Apr 18 11:36:41 2026 +0800

    malloc: Don't call __get_thp_mode/__get_thp_size twice

    Both ld.so and malloc track kernel THP mode and THP page size when THP
    in ld.so is enabled by

    GLIBC_TUNABLES=glibc.elf.thp=1

    and THP in malloc is enabled by

    GLIBC_TUNABLES=glibc.malloc.hugetlb=1

    But DL_MAP_DEFAULT_THP_PAGESIZE and MALLOC_DEFAULT_THP_PAGESIZE may be
    different when they are defined in <hugepages.h>.

    If THP in ld.so is enabled, change malloc to use kernel THP mode from
    ld.so, instead of calling __get_thp_mode, and use THP page size from
    ld.so if it came from __get_thp_size.  This avoids calling __get_thp_mode
    and __get_thp_size again, which are quite expensive:

    1. Initialize mp_.thp_mode and GL(dl_thp_mode) to thp_mode_unknown.
    2. Set mp_.thp_mode to GL(dl_thp_mode) if GL(dl_thp_mode) isn't
    thp_mode_unknown.  Otherwise call __get_thp_mode to set mp_.thp_mode.
    3. GL(dl_elf_thp_pagesize) is set to DL_MAP_DEFAULT_THP_PAGESIZE without
    calling __get_thp_size and THP page size for malloc may be different from
    THP page size for ld.so.  Set mp_.thp_pagesize to GL(dl_elf_thp_pagesize)
    if DL_MAP_DEFAULT_THP_PAGESIZE is defined.  Otherwise call __get_thp_size
    to set mp_.thp_pagesize.
    4. THP page size in malloc is capped to MAX_THP_PAGESIZE.  If THP page
    size is above MAX_THP_PAGESIZE, THP in malloc is disabled.

    These result in when glibc.elf.thp is set to 1, malloc uses the actual
    kernel THP mode instead of defaulting to madvise mode and madvise_thp
    will stop issuing MADV_HUGEPAGE if kernel THP mode is always.

    This fixes BZ #34083.

    Signed-off-by: H.J. Lu <[email protected]>

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