Soft freeze for the glibc-2.44 release
Peter Bergner
bergner@oss.tenstorrent.com
Fri Jul 17 17:34:09 GMT 2026
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
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
--
2.53.0
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