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Refactor purging and splitting/merging.

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Split purging into lazy and forced variants.  Use the forced variant for
zeroing dss.

Add support for NULL function pointers as an opt-out mechanism for the
dalloc, commit, decommit, purge_lazy, purge_forced, split, and merge
fields of extent_hooks_t.

Add short-circuiting checks in large_ralloc_no_move_{shrink,expand}() so
that no attempt is made if splitting/merging is not supported.

This resolves #268.
This commit is contained in:
Jason Evans
2016-12-03 15:38:25 -08:00
parent 884fa22b8c
commit a6e86810d8
11 changed files with 258 additions and 84 deletions
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29
doc/jemalloc.xml.in
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@@ -1512,7 +1512,8 @@ struct extent_hooks_s {
extent_dalloc_t *dalloc;
extent_commit_t *commit;
extent_decommit_t *decommit;
extent_purge_t *purge;
extent_purge_t *purge_lazy;
extent_purge_t *purge_forced;
extent_split_t *split;
extent_merge_t *merge;
};]]></programlisting>
@@ -1522,13 +1523,12 @@ struct extent_hooks_s {
mapped committed memory, in the simplest case followed by deallocation.
However, there are performance and platform reasons to retain extents
for later reuse. Cleanup attempts cascade from deallocation to decommit
to purging, which gives the extent management functions opportunities to
reject the most permanent cleanup operations in favor of less permanent
(and often less costly) operations. The extent splitting and merging
operations can also be opted out of, but this is mainly intended to
support platforms on which virtual memory mappings provided by the
operating system kernel do not automatically coalesce and split, e.g.
Windows.</para>
to lazy purging to forced purging, which gives the extent management
functions opportunities to reject the most permanent cleanup operations
in favor of less permanent (and often less costly) operations. All
operations except allocation can be universally opted out of by setting
the hook pointers to <constant>NULL</constant>, or selectively opted out
of by returning failure.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef void *<function>(extent_alloc_t)</function></funcdef>
@@ -1634,21 +1634,24 @@ struct extent_hooks_s {
<funcdef>typedef bool <function>(extent_purge_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t<parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>offset</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent purge function conforms to the
<type>extent_purge_t</type> type and optionally discards physical pages
<type>extent_purge_t</type> type and discards physical pages
within the virtual memory mapping associated with an extent at given
<parameter>addr</parameter> and <parameter>size</parameter> at
<parameter>offset</parameter> bytes, extending for
<parameter>length</parameter> on behalf of arena
<parameter>arena_ind</parameter>, returning false if pages within the
purged virtual memory range will be zero-filled the next time they are
accessed.</para>
<parameter>arena_ind</parameter>. A lazy extent purge function can
delay purging indefinitely and leave the pages within the purged virtual
memory range in an indeterminite state, whereas a forced extent purge
function immediately purges, and the pages within the virtual memory
range will be zero-filled the next time they are accessed. If the
function returns true, this indicates failure to purge.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_split_t)</function></funcdef>