Soft freeze for the glibc-2.44 release

[Adhemerval Zanella Netto]

On 17/07/26 14:34, Peter Bergner wrote:
> On 7/17/26 11:33 AM, Adhemerval Zanella Netto wrote:
>> I think the safest approach is to revert it and work on having more
>> information for the next release.
> 
> Like the following, which I have yet to build and test, but can do
> when my machine frees up from a different build?  Otherwise, I'm fine
> if someone else wants to revert it for the release.
> 
> Peter

LGTM, thanks.

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

> 
> 
> 
> Revert "malloc: Remove dynamic mmap/trim threshold [BZ #30769]"
> 
> This change causes large degradations on multiple SPEC benchmarks,
> so we have to revert this commit.
> 
> GLIBC BZ: https://sourceware.org/PR34394
> 
> This reverts commit 17a79a51208c5648fe70983085833bf15d83d0f1
> 
> Signed-off-by: Peter Bergner <bergner@tenstorrent.com>
> ---
>  malloc/malloc.c    | 32 ++++++++++++++++++++++++++++----
>  manual/memory.texi | 10 ++++++++--
>  manual/probes.texi | 26 ++++++++++++++++++--------
>  3 files changed, 54 insertions(+), 14 deletions(-)
> 
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 258f203f1e..8fe8b18340 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -1612,6 +1612,10 @@ struct malloc_par
>    int n_mmaps;
>    int n_mmaps_max;
>    int max_n_mmaps;
> +  /* the mmap_threshold is dynamic, until the user sets
> +     it manually, at which point we need to disable any
> +     dynamic behavior. */
> +  int no_dyn_threshold;
>  
>    /* Statistics */
>    INTERNAL_SIZE_T mmapped_mem;
> @@ -4075,6 +4079,18 @@ _int_free_chunk (mstate av, mchunkptr p, INTERNAL_SIZE_T size)
>      /* Preserve errno in case munmap sets it.  */
>      int err = errno;
>  
> +    /* See if the dynamic brk/mmap threshold needs adjusting.
> +       Dumped fake mmapped chunks do not affect the threshold.  */
> +    if (!mp_.no_dyn_threshold
> +        && chunksize_nomask (p) > mp_.mmap_threshold
> +        && chunksize_nomask (p) <= DEFAULT_MMAP_THRESHOLD_MAX)
> +      {
> +        mp_.mmap_threshold = chunksize (p);
> +        mp_.trim_threshold = 2 * mp_.mmap_threshold;
> +        LIBC_PROBE (memory_mallopt_free_dyn_thresholds, 2,
> +		    mp_.mmap_threshold, mp_.trim_threshold);
> +      }
> +
>      munmap_chunk (p);
>  
>      __set_errno (err);
> @@ -4673,32 +4689,40 @@ __malloc_stats (void)
>  static __always_inline int
>  do_set_trim_threshold (size_t value)
>  {
> -  LIBC_PROBE (memory_mallopt_trim_threshold, 2, value, mp_.trim_threshold);
> +  LIBC_PROBE (memory_mallopt_trim_threshold, 3, value, mp_.trim_threshold,
> +	      mp_.no_dyn_threshold);
>    mp_.trim_threshold = value;
> +  mp_.no_dyn_threshold = 1;
>    return 1;
>  }
>  
>  static __always_inline int
>  do_set_top_pad (size_t value)
>  {
> -  LIBC_PROBE (memory_mallopt_top_pad, 2, value, mp_.top_pad);
> +  LIBC_PROBE (memory_mallopt_top_pad, 3, value, mp_.top_pad,
> +	      mp_.no_dyn_threshold);
>    mp_.top_pad = value;
> +  mp_.no_dyn_threshold = 1;
>    return 1;
>  }
>  
>  static __always_inline int
>  do_set_mmap_threshold (size_t value)
>  {
> -  LIBC_PROBE (memory_mallopt_mmap_threshold, 2, value, mp_.mmap_threshold);
> +  LIBC_PROBE (memory_mallopt_mmap_threshold, 3, value, mp_.mmap_threshold,
> +	      mp_.no_dyn_threshold);
>    mp_.mmap_threshold = value;
> +  mp_.no_dyn_threshold = 1;
>    return 1;
>  }
>  
>  static __always_inline int
>  do_set_mmaps_max (int32_t value)
>  {
> -  LIBC_PROBE (memory_mallopt_mmap_max, 2, value, mp_.n_mmaps_max);
> +  LIBC_PROBE (memory_mallopt_mmap_max, 3, value, mp_.n_mmaps_max,
> +	      mp_.no_dyn_threshold);
>    mp_.n_mmaps_max = value;
> +  mp_.no_dyn_threshold = 1;
>    return 1;
>  }
>  
> diff --git a/manual/memory.texi b/manual/memory.texi
> index 744ea6ac64..be0dce0a53 100644
> --- a/manual/memory.texi
> +++ b/manual/memory.texi
> @@ -1333,7 +1333,10 @@ that the memory for these chunks can be returned to the system on
>  @code{free}.  Note that requests smaller than this threshold might still
>  be allocated via @code{mmap}.
>  
> -If this parameter is not set, the default value is set as 128 KiB.
> +If this parameter is not set, the default value is set as 128 KiB and the
> +threshold is adjusted dynamically to suit the allocation patterns of the
> +program. If the parameter is set, the dynamic adjustment is disabled and the
> +value is set statically to the input value.
>  
>  This parameter can also be set for the process at startup by setting the
>  environment variable @env{MALLOC_MMAP_THRESHOLD_} to the desired value.
> @@ -1368,7 +1371,10 @@ environment variable @env{MALLOC_TOP_PAD_} to the desired value.
>  This is the minimum size (in bytes) of the top-most, releasable chunk
>  that will trigger a system call in order to return memory to the system.
>  
> -If this parameter is not set, the default value is set as 128 KiB.
> +If this parameter is not set, the default value is set as 128 KiB and the
> +threshold is adjusted dynamically to suit the allocation patterns of the
> +program. If the parameter is set, the dynamic adjustment is disabled and the
> +value is set statically to the provided input.
>  
>  This parameter can also be set for the process at startup by setting the
>  environment variable @env{MALLOC_TRIM_THRESHOLD_} to the desired value.
> diff --git a/manual/probes.texi b/manual/probes.texi
> index 82d234f4b8..23340e8e07 100644
> --- a/manual/probes.texi
> +++ b/manual/probes.texi
> @@ -161,33 +161,37 @@ value, and @var{$arg2} is the previous value of this @code{malloc}
>  parameter.
>  @end deftp
>  
> -@deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2})
> +@deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
>  This probe is triggered shortly after the @code{memory_mallopt} probe,
>  when the parameter to be changed is @code{M_TRIM_THRESHOLD}.  Argument
>  @var{$arg1} is the requested value, @var{$arg2} is the previous value of
> -this @code{malloc} parameter.
> +this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
> +threshold adjustment was already disabled.
>  @end deftp
>  
> -@deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2})
> +@deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
>  This probe is triggered shortly after the @code{memory_mallopt} probe,
>  when the parameter to be changed is @code{M_TOP_PAD}.  Argument
>  @var{$arg1} is the requested value, @var{$arg2} is the previous value of
> -this @code{malloc} parameter.
> +this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
> +threshold adjustment was already disabled.
>  @end deftp
>  
> -@deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2})
> +@deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
>  This probe is triggered shortly after the @code{memory_mallopt} probe,
>  when the parameter to be changed is @code{M_MMAP_THRESHOLD}, and the
>  requested value is in an acceptable range.  Argument @var{$arg1} is the
>  requested value, @var{$arg2} is the previous value of this @code{malloc}
> -parameter.
> +parameter, and @var{$arg3} is nonzero if dynamic threshold adjustment
> +was already disabled.
>  @end deftp
>  
> -@deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2})
> +@deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
>  This probe is triggered shortly after the @code{memory_mallopt} probe,
>  when the parameter to be changed is @code{M_MMAP_MAX}.  Argument
>  @var{$arg1} is the requested value, @var{$arg2} is the previous value of
> -this @code{malloc} parameter.
> +this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
> +threshold adjustment was already disabled.
>  @end deftp
>  
>  @deftp Probe memory_mallopt_perturb (int @var{$arg1}, int @var{$arg2})
> @@ -213,6 +217,12 @@ requested value, and @var{$arg2} is the previous value of this
>  @code{malloc} parameter.
>  @end deftp
>  
> +@deftp Probe memory_mallopt_free_dyn_thresholds (int @var{$arg1}, int @var{$arg2})
> +This probe is triggered when function @code{free} decides to adjust the
> +dynamic brk/mmap thresholds.  Argument @var{$arg1} and @var{$arg2} are
> +the adjusted mmap and trim thresholds, respectively.
> +@end deftp
> +
>  @deftp Probe memory_tunable_tcache_max_bytes (int @var{$arg1}, int @var{$arg2})
>  This probe is triggered when the @code{glibc.malloc.tcache_max}
>  tunable is set.  Argument @var{$arg1} is the requested value, and