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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2016-10-26 15:05:37 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2016-10-26 15:05:37 +0530
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parentabff18c0c6055ca5d1cd46923fd1205c057139a5 (diff)
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Add note on MALLOC_MMAP_* environment variables
The mallopt parameters manual does not mention the environment variables that can be used to set these parameters at program startup. Mention those environment variables for completeness. * manual/memory.texi: Add environment variable alternatives to setting mallopt parameters.
Diffstat (limited to 'manual/memory.texi')
-rw-r--r--manual/memory.texi36
1 files changed, 36 insertions, 0 deletions
diff --git a/manual/memory.texi b/manual/memory.texi
index 53831053dd9..c6263d20e20 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