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Document under what circumstances in-place resizing succeeds.

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This resolves #100.
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Jason Evans 2015-01-22 15:28:25 -08:00
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commit 228b2e9242
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doc/jemalloc.xml.in
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@ -533,6 +533,22 @@ for (i = 0; i < nbins; i++) {
nearest multiple of the cacheline size, or specify cacheline alignment when nearest multiple of the cacheline size, or specify cacheline alignment when
allocating.</para> allocating.</para>
<para>The <function>realloc<parameter/></function>,
<function>rallocx<parameter/></function>, and
<function>xallocx<parameter/></function> functions may resize allocations
without moving them under limited circumstances. Unlike the
<function>*allocx<parameter/></function> API, the standard API does not
officially round up the usable size of an allocation to the nearest size
class, so technically it is necessary to call
<function>realloc<parameter/></function> to grow e.g. a 9-byte allocation to
16 bytes, or shrink a 16-byte allocation to 9 bytes. Growth and shrinkage
trivially succeeds in place as long as the pre-size and post-size both round
up to the same size class. No other API guarantees are made regarding
in-place resizing, but the current implementation also tries to resize large
and huge allocations in place, as long as the pre-size and post-size are
both large or both huge. In such cases shrinkage always succeeds, but
growth only succeeds if the trailing memory is currently available.</para>
<para>Assuming 4 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit <para>Assuming 4 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit
system, the size classes in each category are as shown in <xref system, the size classes in each category are as shown in <xref
linkend="size_classes" xrefstyle="template:Table %n"/>.</para> linkend="size_classes" xrefstyle="template:Table %n"/>.</para>