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Add support for sized deallocation.

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This adds a new `sdallocx` function to the external API, allowing the
size to be passed by the caller.  It avoids some extra reads in the
thread cache fast path.  In the case where stats are enabled, this
avoids the work of calculating the size from the pointer.

An assertion validates the size that's passed in, so enabling debugging
will allow users of the API to debug cases where an incorrect size is
passed in.

The performance win for a contrived microbenchmark doing an allocation
and immediately freeing it is ~10%.  It may have a different impact on a
real workload.

Closes #28
This commit is contained in:
Daniel Micay 2014-08-28 15:41:48 -04:00 • committed by Jason Evans
parent c3f8650749
commit 4cfe55166e
10 changed files with 201 additions and 5 deletions
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19
doc/jemalloc.xml.in
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@ -38,6 +38,7 @@
<refname>xallocx</refname>
<refname>sallocx</refname>
<refname>dallocx</refname>
<refname>sdallocx</refname>
<refname>nallocx</refname>
<refname>mallctl</refname>
<refname>mallctlnametomib</refname>
@ -120,6 +121,12 @@
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sdallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>size_t <function>nallocx</function></funcdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
@ -228,7 +235,8 @@
<function>rallocx<parameter/></function>,
<function>xallocx<parameter/></function>,
<function>sallocx<parameter/></function>,
<function>dallocx<parameter/></function>, and
<function>dallocx<parameter/></function>,
<function>sdallocx<parameter/></function>, and
<function>nallocx<parameter/></function> functions all have a
<parameter>flags</parameter> argument that can be used to specify
options. The functions only check the options that are contextually
@ -312,6 +320,15 @@
memory referenced by <parameter>ptr</parameter> to be made available for
future allocations.</para>
<para>The <function>sdallocx<parameter/></function> function is an
extension of <function>dallocx<parameter/></function> with a
<parameter>size</parameter> parameter to allow the caller to pass in the
allocation size as an optimization. The minimum valid input size is the
original requested size of the allocation, and the maximum valid input
size is the corresponding value returned by
<function>nallocx<parameter/></function> or
<function>sallocx<parameter/></function>.</para>
<para>The <function>nallocx<parameter/></function> function allocates no
memory, but it performs the same size computation as the
<function>mallocx<parameter/></function> function, and returns the real