PING: [PATCH] malloc: Don't call __get_thp_mode/__get_thp_size twice

[H.J. Lu]

On Wed, Jun 17, 2026 at 6:58 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> This patch is on top of
>
> commit 8c84793bab32868e557615c2e74b65ea06c0cd85
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Mon Apr 13 08:23:05 2026 +0800
>
>     elf: Support THP segment load with madvise enabled THP
>
> https://patchwork.sourceware.org/project/glibc/list/?series=62321

This patch has been merged into master branch.

> --
> 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.
>
> This fixes BZ #34083.
>
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> ---
>  malloc/malloc.c             | 56 +++++++++++++++++++++++++++++++++----
>  sysdeps/generic/hugepages.h |  3 +-
>  2 files changed, 53 insertions(+), 6 deletions(-)
>
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index a354576aca..f0ed95213f 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -1529,7 +1529,7 @@ static struct malloc_par mp_ =
>    .mmap_threshold = DEFAULT_MMAP_THRESHOLD,
>    .trim_threshold = DEFAULT_TRIM_THRESHOLD,
>    .arena_test = sizeof (long) == 4 ? 2 : 8,
> -  .thp_mode = thp_mode_not_supported
> +  .thp_mode = thp_mode_unknown
>  #if USE_TCACHE
>    ,
>    .tcache_count = TCACHE_FILL_COUNT,
> @@ -4657,13 +4657,41 @@ do_set_mxfast (size_t value)
>    return 1;
>  }
>
> +#ifdef HAVE_THP
> +static __always_inline enum thp_mode_t
> +get_dl_thp_mode (void)
> +{
> +  return GL(dl_thp_mode);
> +}
> +
> +static __always_inline unsigned long int
> +get_dl_elf_thp_pagesize (void)
> +{
> +  return GL(dl_elf_thp_pagesize);
> +}
> +#else
> +# define get_dl_thp_mode()             __get_thp_mode ()
> +# define get_dl_elf_thp_pagesize()     __get_thp_size ()
> +#endif
> +
>  static __always_inline int
>  do_set_hugetlb (size_t value)
>  {
> +  /* If __get_thp_mode and __get_thp_size have been called during
> +     startup, don't call them again here.  */
> +  enum thp_mode_t thp_mode = get_dl_thp_mode ();
> +
>    /* Enable THP if MALLOC_DEFAULT_THP_PAGESIZE is non-zero.  */
>    if (MALLOC_DEFAULT_THP_PAGESIZE > 0)
>      {
> -      mp_.thp_mode = thp_mode_madvise;
> +      /* If thp_mode is unknown, THP segment load is disabled by
> +        GLIBC_TUNABLES=glibc.elf.thp=0.  In this case, set
> +        mp_.thp_mode to madvise.  Otherwise, set it to thp_mode to
> +        keep mp_.thp_mode in sync with GL(dl_thp_mode).  */
> +      if (thp_mode == thp_mode_unknown)
> +       mp_.thp_mode = thp_mode_madvise;
> +      else
> +       mp_.thp_mode = thp_mode;
>        mp_.thp_pagesize = MALLOC_DEFAULT_THP_PAGESIZE;
>      }
>
> @@ -4680,9 +4708,27 @@ do_set_hugetlb (size_t value)
>        if (MALLOC_DEFAULT_THP_PAGESIZE > 0)
>         return 0;
>
> -      mp_.thp_mode = __get_thp_mode ();
> -      if (mp_.thp_mode == thp_mode_madvise || mp_.thp_mode == thp_mode_always)
> -       mp_.thp_pagesize = __get_thp_size ();
> +      if (thp_mode == thp_mode_unknown)
> +       {
> +         /* Call __get_thp_mode and __get_thp_size when THP segment load
> +            is disabled.  */
> +         mp_.thp_mode = __get_thp_mode ();
> +         if (mp_.thp_mode == thp_mode_madvise
> +             || mp_.thp_mode == thp_mode_always)
> +           mp_.thp_pagesize = __get_thp_size ();
> +       }
> +      else
> +       {
> +         /* THP segment load is enabled.  GL(dl_elf_thp_pagesize) is
> +            set to DL_MAP_DEFAULT_THP_PAGESIZE if it isn't zero .  In
> +            this case, call __get_thp_size () instead of using
> +            DL_MAP_DEFAULT_THP_PAGESIZE for malloc.  */
> +         mp_.thp_mode = thp_mode;
> +         if (DL_MAP_DEFAULT_THP_PAGESIZE != 0)
> +           mp_.thp_pagesize = __get_thp_size ();
> +         else
> +           mp_.thp_pagesize = get_dl_elf_thp_pagesize ();
> +       }
>      }
>    else if (value >= 2)
>      __get_hugepage_config (value == 2 ? 0 : value, &mp_.hp_pagesize,
> diff --git a/sysdeps/generic/hugepages.h b/sysdeps/generic/hugepages.h
> index 8e54661527..49251d94ab 100644
> --- a/sysdeps/generic/hugepages.h
> +++ b/sysdeps/generic/hugepages.h
> @@ -37,7 +37,8 @@ unsigned long int __get_thp_size (void) attribute_hidden;
>
>  enum thp_mode_t
>  {
> -  thp_mode_not_supported = 0,
> +  thp_mode_unknown = 0,
> +  thp_mode_not_supported,
>    thp_mode_always,
>    thp_mode_madvise,
>    thp_mode_never
> --
> 2.54.0
>


-- 
H.J.