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Diffstat (limited to 'manual')
| -rw-r--r-- | manual/memory.texi | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/manual/memory.texi b/manual/memory.texi index 53831053dd..c6263d20e2 100644 --- a/manual/memory.texi +++ b/manual/memory.texi @@ -1113,13 +1113,28 @@ choices for @var{param}, as defined in @file{malloc.h}, are: @item M_MMAP_MAX The maximum number of chunks to allocate with @code{mmap}. Setting this to zero disables all use of @code{mmap}. + +The default value of this parameter is @code{65536}. + +This parameter can also be set for the process at startup by setting the +environment variable @env{MALLOC_MMAP_MAX_} to the desired value. + @item M_MMAP_THRESHOLD All chunks larger than this value are allocated outside the normal heap, using the @code{mmap} system call. This way it is guaranteed 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 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. @comment TODO: @item M_MXFAST + @item M_PERTURB If non-zero, memory blocks are filled with values depending on some low order bits of this parameter when they are allocated (except when @@ -1128,16 +1143,37 @@ use of uninitialized or freed heap memory. Note that this option does not guarantee that the freed block will have any specific values. It only guarantees that the content the block had before it was freed will be overwritten. + +The default value of this parameter is @code{0}. + +This parameter can also be set for the process at startup by setting the +environment variable @env{MALLOC_MMAP_PERTURB_} to the desired value. + @item M_TOP_PAD This parameter determines the amount of extra memory to obtain from the system when a call to @code{sbrk} is required. It also specifies the number of bytes to retain when shrinking the heap by calling @code{sbrk} with a negative argument. This provides the necessary hysteresis in heap size such that excessive amounts of system calls can be avoided. + +The default value of this parameter is @code{0}. + +This parameter can also be set for the process at startup by setting the +environment variable @env{MALLOC_TOP_PAD_} to the desired value. + @item M_TRIM_THRESHOLD This is the minimum size (in bytes) of the top-most, releasable chunk that will cause @code{sbrk} to be called with a negative argument in order to return memory to the system. + +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. + @end table @end deftypefun |