[PATCH] thp: Disable THP if THP isn't supported by kernel

[Adhemerval Zanella Netto]

On 04/07/26 00:05, H.J. Lu wrote:
> Since DL_MAP_DEFAULT_THP_PAGESIZE is defined for x86-64, THP control
> is to set to madvise by default.  If THP is disabled in x86-64 kernel,
> madvise (..., MADV_HUGEPAGE) returns -EINVAL to indicate that THP isn't
> supported.  Add _dl_thp_madvise to disable THP in this case.  This
> fixes BZ #34348.
> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>

LGTM, two suggestion below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  sysdeps/unix/sysv/linux/dl-exec-post.h   |  6 ++--
>  sysdeps/unix/sysv/linux/dl-load-post.h   |  6 ++--
>  sysdeps/unix/sysv/linux/dl-thp-madvise.h | 35 ++++++++++++++++++++++++
>  3 files changed, 43 insertions(+), 4 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/dl-thp-madvise.h
> 
> diff --git a/sysdeps/unix/sysv/linux/dl-exec-post.h b/sysdeps/unix/sysv/linux/dl-exec-post.h
> index 9a49486db2..4bc8a50dd1 100644
> --- a/sysdeps/unix/sysv/linux/dl-exec-post.h
> +++ b/sysdeps/unix/sysv/linux/dl-exec-post.h
> @@ -17,6 +17,8 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> +#include "dl-thp-madvise.h"
> +
>  static inline void
>  _dl_get_thp_config (void)
>  {
> @@ -116,8 +118,8 @@ _dl_executable_postprocess (struct link_map *main_map,
>  	&& ((ph->p_vaddr | ph->p_offset) & (thp_pagesize - 1)) == 0
>  	&& (ph->p_flags & (PF_W | PF_R)) == PF_R)
>        {
> -	int ret = __madvise ((void *) (main_map->l_addr + ph->p_vaddr),
> -			     ph->p_memsz, MADV_HUGEPAGE);
> +	void *addr = (void *) (main_map->l_addr + ph->p_vaddr);
> +	int ret = _dl_thp_madvise (addr, ph->p_memsz);
>  	if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
>  	  _dl_debug_printf ("\
>  madvise (0x%0*lx, 0x%0*lx, MADV_HUGEPAGE) returns %d\n",
> diff --git a/sysdeps/unix/sysv/linux/dl-load-post.h b/sysdeps/unix/sysv/linux/dl-load-post.h
> index 741c4ddcb1..935298bda5 100644
> --- a/sysdeps/unix/sysv/linux/dl-load-post.h
> +++ b/sysdeps/unix/sysv/linux/dl-load-post.h
> @@ -17,6 +17,8 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> +#include "dl-thp-madvise.h"
> +
>  static bool _dl_segment_thp_eligible (const struct loadcmd *, size_t);
>  
>  /* After L has been mapped in, call madvise with MADV_HUGEPAGE for THP
> @@ -28,8 +30,8 @@ _dl_postprocess_loadcmd_extra (struct link_map *l, const struct loadcmd *c)
>    if (GL(dl_thp_mode) == thp_mode_madvise
>        && _dl_segment_thp_eligible (c, GL(dl_elf_thp_pagesize)))
>      {
> -      int ret = __madvise ((void *) (l->l_addr + c->mapstart),
> -			   c->mapend - c->mapstart, MADV_HUGEPAGE);
> +      int ret = _dl_thp_madvise ((void *) (l->l_addr + c->mapstart),
> +				 c->mapend - c->mapstart);
>        if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
>  	_dl_debug_printf ("\
>    madvise (0x%0*lx, 0x%0*lx, MADV_HUGEPAGE) returns %d\n",
> diff --git a/sysdeps/unix/sysv/linux/dl-thp-madvise.h b/sysdeps/unix/sysv/linux/dl-thp-madvise.h
> new file mode 100644
> index 0000000000..1d54d19987
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/dl-thp-madvise.h
> @@ -0,0 +1,35 @@
> +/* _dl_thp_madvise.  Linux version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   Copyright The GNU Toolchain Authors.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */

Maybe a guard include here.

> +
> +/* Similar to madvise, but disable THP if the madvise syscall returns
> +   -EINVAL which indicates that THP isn't supported by kernel.  */
> +
> +static inline int
> +_dl_thp_madvise (void *addr, size_t size)
> +{
> +  int res = INTERNAL_SYSCALL_CALL (madvise, addr, size, MADV_HUGEPAGE);
> +  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res))
> +      && INTERNAL_SYSCALL_ERRNO (res) == EINVAL)
> +    {
> +      /* NB: Disable THP if THP isn't supported by kernel.  */
> +      GL(dl_thp_mode) = thp_mode_not_supported;
> +      GL(dl_elf_thp_control) = dl_elf_thp_control_disabled;
> +    }
> +  return res;

This changes the DL_DEBUG_FILES to print the -errno value insteaf of the
-1 previously, which is an improvement but a bit confusing.  Maybe return
INTERNAL_SYSCALL_ERRNO.

> +}