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authorxsipewe <[email protected]>2016-06-21 15:50:34 +0200
committerLukas Larsson <[email protected]>2016-07-13 11:30:48 +0200
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tree3f1550c75327118ad0255220344ee43313f52a67 /erts/doc/src/erts_alloc.xml
parentd281213a4a04a61910a6c451d8f5c86e61416bb2 (diff)
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erts: Editorial changes
Diffstat (limited to 'erts/doc/src/erts_alloc.xml')
-rw-r--r--erts/doc/src/erts_alloc.xml1101
1 files changed, 615 insertions, 486 deletions
diff --git a/erts/doc/src/erts_alloc.xml b/erts/doc/src/erts_alloc.xml
index 9aef1c0b1f..c1706806fe 100644
--- a/erts/doc/src/erts_alloc.xml
+++ b/erts/doc/src/erts_alloc.xml
@@ -25,63 +25,68 @@
<title>erts_alloc</title>
<prepared>Rickard Green</prepared>
<docno>1</docno>
- <date>03-06-11</date>
+ <date>2003-06-11</date>
<rev>1</rev>
<file>erts_alloc.xml</file>
</header>
<lib>erts_alloc</lib>
- <libsummary>An Erlang Run-Time System internal memory allocator library.</libsummary>
+ <libsummary>An Erlang runtime system internal memory allocator library.
+ </libsummary>
<description>
- <p><c>erts_alloc</c> is an Erlang Run-Time System internal memory
+ <p><c>erts_alloc</c> is an Erlang runtime system internal memory
allocator library. <c>erts_alloc</c> provides the Erlang
- Run-Time System with a number of memory allocators.</p>
+ runtiime system with a number of memory allocators.</p>
</description>
<section>
<title>Allocators</title>
<marker id="allocators"></marker>
- <p>Currently the following allocators are present:</p>
+ <p>The following allocators are present:</p>
+
<taglist>
<tag><c>temp_alloc</c></tag>
<item>Allocator used for temporary allocations.</item>
<tag><c>eheap_alloc</c></tag>
- <item>Allocator used for Erlang heap data, such as Erlang process heaps.</item>
+ <item>Allocator used for Erlang heap data, such as Erlang process heaps.
+ </item>
<tag><c>binary_alloc</c></tag>
<item>Allocator used for Erlang binary data.</item>
<tag><c>ets_alloc</c></tag>
- <item>Allocator used for ETS data.</item>
+ <item>Allocator used for <c>ets</c> data.</item>
<tag><c>driver_alloc</c></tag>
<item>Allocator used for driver data.</item>
<tag><c>literal_alloc</c></tag>
<item>Allocator used for constant terms in Erlang code.</item>
<tag><c>sl_alloc</c></tag>
<item>Allocator used for memory blocks that are expected to be
- short-lived.</item>
+ short-lived.</item>
<tag><c>ll_alloc</c></tag>
<item>Allocator used for memory blocks that are expected to be
- long-lived, for example Erlang code.</item>
+ long-lived, for example, Erlang code.</item>
<tag><c>fix_alloc</c></tag>
<item>A fast allocator used for some frequently used
fixed size data types.</item>
<tag><c>exec_alloc</c></tag>
- <item>Allocator used by hipe for native executable code
- on specific architectures (x86_64).</item>
+ <item>Allocator used by the <seealso marker="hipe"><c>HiPE</c></seealso>
+ application for native executable code on specific architectures
+ (x86_64).</item>
<tag><c>std_alloc</c></tag>
- <item>Allocator used for most memory blocks not allocated via any of
- the other allocators described above.</item>
+ <item>Allocator used for most memory blocks not allocated through any of
+ the other allocators described above.</item>
<tag><c>sys_alloc</c></tag>
<item>This is normally the default <c>malloc</c> implementation
- used on the specific OS.</item>
+ used on the specific OS.</item>
<tag><c>mseg_alloc</c></tag>
- <item>A memory segment allocator. <c>mseg_alloc</c> is used by other
- allocators for allocating memory segments and is currently only
- available on systems that have the <c>mmap</c> system
- call. Memory segments that are deallocated are kept for a
- while in a segment cache before they are destroyed. When
- segments are allocated, cached segments are used if possible
- instead of creating new segments. This in order to reduce
- the number of system calls made.</item>
+ <item>A memory segment allocator. It is used by other
+ allocators for allocating memory segments and is only
+ available on systems that have the <c>mmap</c> system
+ call. Memory segments that are deallocated are kept for a
+ while in a segment cache before they are destroyed. When
+ segments are allocated, cached segments are used if possible
+ instead of creating new segments. This to reduce
+ the number of system calls made.</item>
</taglist>
+
<p><c>sys_alloc</c> and <c>literal_alloc</c> are always enabled and
cannot be disabled. <c>exec_alloc</c> is only available if it is needed
and cannot be disabled. <c>mseg_alloc</c> is always enabled if it is
@@ -90,9 +95,10 @@
By default all allocators are enabled.
When an allocator is disabled, <c>sys_alloc</c> is used instead of
the disabled allocator.</p>
+
<p>The main idea with the <c>erts_alloc</c> library is to separate
memory blocks that are used differently into different memory
- areas, and by this achieving less memory fragmentation. By
+ areas, to achieve less memory fragmentation. By
putting less effort in finding a good fit for memory blocks that
are frequently allocated than for those less frequently
allocated, a performance gain can be achieved.</p>
@@ -100,61 +106,85 @@
<section>
<marker id="alloc_util"></marker>
- <title>The alloc_util framework</title>
+ <title>The alloc_util Framework</title>
<p>Internally a framework called <c>alloc_util</c> is used for
- implementing allocators. <c>sys_alloc</c>, and
- <c>mseg_alloc</c> do not use this framework; hence, the
+ implementing allocators. <c>sys_alloc</c> and
+ <c>mseg_alloc</c> do not use this framework, so the
following does <em>not</em> apply to them.</p>
+
<p>An allocator manages multiple areas, called carriers, in which
memory blocks are placed. A carrier is either placed in a
- separate memory segment (allocated via <c>mseg_alloc</c>), or in
- the heap segment (allocated via <c>sys_alloc</c>). Multiblock
- carriers are used for storage of several blocks. Singleblock
- carriers are used for storage of one block. Blocks that are
- larger than the value of the singleblock carrier threshold
- (<seealso marker="#M_sbct">sbct</seealso>) parameter are placed
- in singleblock carriers. Blocks that are smaller than the value
- of the <c>sbct</c> parameter are placed in multiblock
- carriers. Normally an allocator creates a "main multiblock
+ separate memory segment (allocated through <c>mseg_alloc</c>), or in
+ the heap segment (allocated through <c>sys_alloc</c>).</p>
+
+ <list type="bulleted">
+ <item>
+ <p>Multiblock carriers are used for storage of several blocks.</p>
+ </item>
+ <item>
+ <p>Singleblock carriers are used for storage of one block.</p>
+ </item>
+ <item>
+ <p>Blocks that are larger than the value of the singleblock carrier
+ threshold (<seealso marker="#M_sbct"><c>sbct</c></seealso>) parameter
+ are placed in singleblock carriers.</p>
+ </item>
+ <item>
+ <p>Blocks that are smaller than the value of parameter <c>sbct</c>
+ are placed in multiblock carriers.</p></item>
+ </list>
+
+ <p>Normally an allocator creates a "main multiblock
carrier". Main multiblock carriers are never deallocated. The
- size of the main multiblock carrier is determined by the value
- of the <seealso marker="#M_mmbcs">mmbcs</seealso> parameter.</p>
+ size of the main multiblock carrier is determined by the value of
+ parameter <seealso marker="#M_mmbcs"><c>mmbcs</c></seealso>.</p>
+
<p><marker id="mseg_mbc_sizes"></marker>Sizes of multiblock carriers
- allocated via <c>mseg_alloc</c> are
- decided based on the values of the largest multiblock carrier
- size (<seealso marker="#M_lmbcs">lmbcs</seealso>), the smallest
- multiblock carrier size (<seealso marker="#M_smbcs">smbcs</seealso>),
- and the multiblock carrier growth stages
- (<seealso marker="#M_mbcgs">mbcgs</seealso>) parameters. If
- <c>nc</c> is the current number of multiblock carriers (the main
+ allocated through <c>mseg_alloc</c> are decided based on the
+ following parameters:</p>
+
+ <list type="bulleted">
+ <item>The values of the largest multiblock carrier size
+ (<seealso marker="#M_lmbcs"><c>lmbcs</c></seealso>)</item>
+ <item>The smallest multiblock carrier size
+ (<seealso marker="#M_smbcs"><c>smbcs</c></seealso>)</item>
+ <item>The multiblock carrier growth stages
+ (<seealso marker="#M_mbcgs"><c>mbcgs</c></seealso>)</item>
+ </list>
+
+ <p>If <c>nc</c> is the current number of multiblock carriers (the main
multiblock carrier excluded) managed by an allocator, the size
of the next <c>mseg_alloc</c> multiblock carrier allocated by
- this allocator will roughly be
+ this allocator is roughly
<c><![CDATA[smbcs+nc*(lmbcs-smbcs)/mbcgs]]></c> when
<c><![CDATA[nc <= mbcgs]]></c>,
- and <c>lmbcs</c> when <c><![CDATA[nc > mbcgs]]></c>. If the value of the
- <c>sbct</c> parameter should be larger than the value of the
- <c>lmbcs</c> parameter, the allocator may have to create
- multiblock carriers that are larger than the value of the
- <c>lmbcs</c> parameter, though.
- Singleblock carriers allocated via <c>mseg_alloc</c> are sized
+ and <c>lmbcs</c> when <c><![CDATA[nc > mbcgs]]></c>. If the value of
+ parameter <c>sbct</c> is larger than the value of parameter
+ <c>lmbcs</c>, the allocator may have to create
+ multiblock carriers that are larger than the value of
+ parameter <c>lmbcs</c>, though.
+ Singleblock carriers allocated through <c>mseg_alloc</c> are sized
to whole pages.</p>
- <p>Sizes of carriers allocated via <c>sys_alloc</c> are
+
+ <p>Sizes of carriers allocated through <c>sys_alloc</c> are
decided based on the value of the <c>sys_alloc</c> carrier size
- (<seealso marker="#Muycs">ycs</seealso>) parameter. The size of
- a carrier is the least number of multiples of the value of the
- <c>ycs</c> parameter that satisfies the request.</p>
+ (<seealso marker="#Muycs"><c>ycs</c></seealso>) parameter. The size of
+ a carrier is the least number of multiples of the value of
+ parameter <c>ycs</c> satisfying the request.</p>
+
<p>Coalescing of free blocks are always performed immediately.
- Boundary tags (headers and footers) in free blocks are used
+ Boundary tags (headers and footers) in free blocks are used,
which makes the time complexity for coalescing constant.</p>
+
<p><marker id="strategy"></marker>The memory allocation strategy
- used for multiblock carriers by an
- allocator is configurable via the <seealso marker="#M_as">as</seealso>
- parameter. Currently the following strategies are available:</p>
+ used for multiblock carriers by an allocator can be
+ configured using parameter <seealso marker="#M_as"><c>as</c></seealso>.
+ The following strategies are available:</p>
+
<taglist>
<tag>Best fit</tag>
<item>
- <p>Strategy: Find the smallest block that satisfies the
+ <p>Strategy: Find the smallest block satisfying the
requested block size.</p>
<p>Implementation: A balanced binary search tree is
used. The time complexity is proportional to log N, where
@@ -162,7 +192,7 @@
</item>
<tag>Address order best fit</tag>
<item>
- <p>Strategy: Find the smallest block that satisfies the
+ <p>Strategy: Find the smallest block satisfying the
requested block size. If multiple blocks are found, choose
the one with the lowest address.</p>
<p>Implementation: A balanced binary search tree is
@@ -171,7 +201,7 @@
</item>
<tag>Address order first fit</tag>
<item>
- <p>Strategy: Find the block with the lowest address that satisfies the
+ <p>Strategy: Find the block with the lowest address satisfying the
requested block size.</p>
<p>Implementation: A balanced binary search tree is
used. The time complexity is proportional to log N, where
@@ -180,8 +210,8 @@
<tag>Address order first fit carrier best fit</tag>
<item>
<p>Strategy: Find the <em>carrier</em> with the lowest address that
- can satisfy the requested block size, then find a block within
- that carrier using the "best fit" strategy.</p>
+ can satisfy the requested block size, then find a block within
+ that carrier using the "best fit" strategy.</p>
<p>Implementation: Balanced binary search trees are
used. The time complexity is proportional to log N, where
N is the number of free blocks.</p>
@@ -189,8 +219,8 @@
<tag>Address order first fit carrier address order best fit</tag>
<item>
<p>Strategy: Find the <em>carrier</em> with the lowest address that
- can satisfy the requested block size, then find a block within
- that carrier using the "adress order best fit" strategy.</p>
+ can satisfy the requested block size, then find a block within
+ that carrier using the "address order best fit" strategy.</p>
<p>Implementation: Balanced binary search trees are
used. The time complexity is proportional to log N, where
N is the number of free blocks.</p>
@@ -200,12 +230,12 @@
<p>Strategy: Try to find the best fit, but settle for the best fit
found during a limited search.</p>
<p>Implementation: The implementation uses segregated free
- lists with a maximum block search depth (in each list) in
- order to find a good fit fast. When the maximum block
- search depth is small (by default 3) this implementation
+ lists with a maximum block search depth (in each list)
+ to find a good fit fast. When the maximum block
+ search depth is small (by default 3), this implementation
has a time complexity that is constant. The maximum block
- search depth is configurable via the
- <seealso marker="#M_mbsd">mbsd</seealso> parameter.</p>
+ search depth can be configured using parameter
+ <seealso marker="#M_mbsd"><c>mbsd</c></seealso>.</p>
</item>
<tag>A fit</tag>
<item>
@@ -213,43 +243,47 @@
block to see if it satisfies the request. This strategy is
only intended to be used for temporary allocations.</p>
<p>Implementation: Inspect the first block in a free-list.
- If it satisfies the request, it is used; otherwise, a new
+ If it satisfies the request, it is used, otherwise a new
carrier is created. The implementation has a time
complexity that is constant.</p>
- <p>As of erts version 5.6.1 the emulator will refuse to
- use this strategy on other allocators than <c>temp_alloc</c>.
- This since it will only cause problems for other allocators.</p>
+ <p>As from <c>ERTS</c> 5.6.1 the emulator refuses to
+ use this strategy on other allocators than <c>temp_alloc</c>.
+ This because it only causes problems for other allocators.</p>
</item>
</taglist>
- <p>Apart from the ordinary allocators described above a number of
- pre-allocators are used for some specific data types. These
- pre-allocators pre-allocate a fixed amount of memory for certain data
- types when the run-time system starts. As long as pre-allocated memory
- is available, it will be used. When no pre-allocated memory is
- available, memory will be allocated in ordinary allocators. These
- pre-allocators are typically much faster than the ordinary allocators,
- but can only satisfy a limited amount of requests.</p>
+
+ <p>Apart from the ordinary allocators described above, some
+ pre-allocators are used for some specific data types. These
+ pre-allocators pre-allocate a fixed amount of memory for certain data
+ types when the runtime system starts. As long as pre-allocated memory
+ is available, it is used. When no pre-allocated memory is
+ available, memory is allocated in ordinary allocators. These
+ pre-allocators are typically much faster than the ordinary allocators,
+ but can only satisfy a limited number of requests.</p>
</section>
<section>
<marker id="flags"></marker>
<title>System Flags Effecting erts_alloc</title>
<warning>
- <p>Only use these flags if you are absolutely sure what you are
- doing. Unsuitable settings may cause serious performance
+ <p>Only use these flags if you are sure what you are
+ doing. Unsuitable settings can cause serious performance
degradation and even a system crash at any time during
operation.</p>
</warning>
+
<p>Memory allocator system flags have the following syntax:
- <c><![CDATA[+M<S><P> <V>]]></c>
+ <c><![CDATA[+M<S><P> <V>]]></c>,
where <c><![CDATA[<S>]]></c> is a letter identifying a subsystem,
<c><![CDATA[<P>]]></c> is a parameter, and <c><![CDATA[<V>]]></c> is the
value to use. The flags can be passed to the Erlang emulator
- (<seealso marker="erl">erl</seealso>) as command line
+ (<seealso marker="erl"><c>erl(1)</c></seealso>) as command-line
arguments.</p>
- <p>System flags effecting specific allocators have an upper-case
+
+ <p>System flags effecting specific allocators have an uppercase
letter as <c><![CDATA[<S>]]></c>. The following letters are used for
- the currently present allocators:</p>
+ the allocators:</p>
+
<list type="bulleted">
<item><c>B: binary_alloc</c></item>
<item><c>D: std_alloc</c></item>
@@ -265,421 +299,516 @@
<item><c>X: exec_alloc</c></item>
<item><c>Y: sys_alloc</c></item>
</list>
- <p>The following flags are available for configuration of
- <c>mseg_alloc</c>:</p>
- <taglist>
- <tag><marker id="MMamcbf"/><c><![CDATA[+MMamcbf <size>]]></c></tag>
- <item>
- Absolute max cache bad fit (in kilobytes). A segment in the
- memory segment cache is not reused if its size exceeds the
- requested size with more than the value of this
- parameter. Default value is 4096. </item>
- <tag><marker id="MMrmcbf"/><c><![CDATA[+MMrmcbf <ratio>]]></c></tag>
- <item>
- Relative max cache bad fit (in percent). A segment in the
- memory segment cache is not reused if its size exceeds the
- requested size with more than relative max cache bad fit
- percent of the requested size. Default value is 20.</item>
- <tag><marker id="MMsco"/><c><![CDATA[+MMsco true|false]]></c></tag>
- <item>
- Set <seealso marker="#MMscs">super carrier</seealso> only flag. This
- flag defaults to <c>true</c>. When a super carrier is used and this
- flag is <c>true</c>, <c>mseg_alloc</c> will only create carriers
- in the super carrier. Note that the <c>alloc_util</c> framework may
- create <c>sys_alloc</c> carriers, so if you want all carriers to
- be created in the super carrier, you therefore want to disable use
- of <c>sys_alloc</c> carriers by also passing
- <seealso marker="#Musac"><c>+Musac false</c></seealso>. When the flag
- is <c>false</c>, <c>mseg_alloc</c> will try to create carriers outside
- of the super carrier when the super carrier is full.
- <br/><br/>
- <em>NOTE</em>: Setting this flag to <c>false</c> may not be supported
- on all systems. This flag will in that case be ignored.
- <br/><br/>
- <em>NOTE</em>: The super carrier cannot be enabled nor
- disabled on halfword heap systems. This flag will be
- ignored on halfword heap systems.
- </item>
- <tag><marker id="MMscrfsd"/><c><![CDATA[+MMscrfsd <amount>]]></c></tag>
- <item>
- Set <seealso marker="#MMscs">super carrier</seealso> reserved
- free segment descriptors. This parameter defaults to <c>65536</c>.
- This parameter determines the amount of memory to reserve for
- free segment descriptors used by the super carrier. If the system
- runs out of reserved memory for free segment descriptors, other
- memory will be used. This may however cause fragmentation issues,
- so you want to ensure that this never happens. The maximum amount
- of free segment descriptors used can be retrieved from the
- <c>erts_mmap</c> tuple part of the result from calling
- <seealso marker="erts:erlang#system_info_allocator_tuple">erlang:system_info({allocator, mseg_alloc})</seealso>.
- </item>
- <tag><marker id="MMscrpm"/><c><![CDATA[+MMscrpm true|false]]></c></tag>
- <item>
- Set <seealso marker="#MMscs">super carrier</seealso> reserve physical
- memory flag. This flag defaults to <c>true</c>. When this flag is
- <c>true</c>, physical memory will be reserved for the whole super
- carrier at once when it is created. The reservation will after that
- be left unchanged. When this flag is set to <c>false</c> only virtual
- address space will be reserved for the super carrier upon creation.
- The system will attempt to reserve physical memory upon carrier
- creations in the super carrier, and attempt to unreserve physical
- memory upon carrier destructions in the super carrier.
- <br/><br/>
- <em>NOTE</em>: What reservation of physical memory actually means
- highly depends on the operating system, and how it is configured. For
- example, different memory overcommit settings on Linux drastically
- change the behaviour. Also note, setting this flag to <c>false</c>
- may not be supported on all systems. This flag will in that case
- be ignored.
- <br/><br/>
- <em>NOTE</em>: The super carrier cannot be enabled nor
- disabled on halfword heap systems. This flag will be
- ignored on halfword heap systems.
- </item>
- <tag><marker id="MMscs"/><c><![CDATA[+MMscs <size in MB>]]></c></tag>
- <item>
- Set super carrier size (in MB). The super carrier size defaults to
- zero; i.e, the super carrier is by default disabled. The super
- carrier is a large continuous area in the virtual address space.
- <c>mseg_alloc</c> will always try to create new carriers in the super
- carrier if it exists. Note that the <c>alloc_util</c> framework may
- create <c>sys_alloc</c> carriers. For more information on this, see the
- documentation of the <seealso marker="#MMsco"><c>+MMsco</c></seealso>
- flag.
- <br/><br/>
- <em>NOTE</em>: The super carrier cannot be enabled nor
- disabled on halfword heap systems. This flag will be
- ignored on halfword heap systems.
- </item>
- <tag><marker id="MMmcs"/><c><![CDATA[+MMmcs <amount>]]></c></tag>
- <item>
- Max cached segments. The maximum number of memory segments
- stored in the memory segment cache. Valid range is
- 0-30. Default value is 10.</item>
- </taglist>
- <p>The following flags are available for configuration of
- <c>sys_alloc</c>:</p>
- <taglist>
- <tag><marker id="MYe"/><c>+MYe true</c></tag>
- <item>
- Enable <c>sys_alloc</c>. Note: <c>sys_alloc</c> cannot be disabled.</item>
- <tag><marker id="MYm"/><c>+MYm libc</c></tag>
- <item>
- <c>malloc</c> library to use. Currently only
- <c>libc</c> is available. <c>libc</c> enables the standard
- <c>libc</c> malloc implementation. By default <c>libc</c> is used.</item>
- <tag><marker id="MYtt"/><c><![CDATA[+MYtt <size>]]></c></tag>
- <item>
- Trim threshold size (in kilobytes). This is the maximum amount
- of free memory at the top of the heap (allocated by
- <c>sbrk</c>) that will be kept by <c>malloc</c> (not
- released to the operating system). When the amount of free
- memory at the top of the heap exceeds the trim threshold,
- <c>malloc</c> will release it (by calling
- <c>sbrk</c>). Trim threshold is given in kilobytes. Default
- trim threshold is 128. <em>Note:</em> This flag will
- only have any effect when the emulator has been linked with
- the GNU C library, and uses its <c>malloc</c> implementation.</item>
- <tag><marker id="MYtp"/><c><![CDATA[+MYtp <size>]]></c></tag>
- <item>
- Top pad size (in kilobytes). This is the amount of extra
- memory that will be allocated by <c>malloc</c> when
- <c>sbrk</c> is called to get more memory from the operating
- system. Default top pad size is 0. <em>Note:</em> This flag
- will only have any effect when the emulator has been linked
- with the GNU C library, and uses its <c>malloc</c>
- implementation.</item>
- </taglist>
- <p>The following flags are available for configuration of allocators
- based on <c>alloc_util</c>. If <c>u</c> is used as subsystem
- identifier (i.e., <c><![CDATA[<S> = u]]></c>) all allocators based on
- <c>alloc_util</c> will be effected. If <c>B</c>, <c>D</c>, <c>E</c>,
- <c>F</c>, <c>H</c>, <c>L</c>, <c>R</c>, <c>S</c>, or <c>T</c> is used as
- subsystem identifier, only the specific allocator identified will be
- effected:</p>
- <taglist>
- <tag><marker id="M_acul"/><c><![CDATA[+M<S>acul <utilization>|de]]></c></tag>
- <item>
- Abandon carrier utilization limit. A valid
- <c><![CDATA[<utilization>]]></c> is an integer in the range
- <c>[0, 100]</c> representing utilization in percent. When a
- utilization value larger than zero is used, allocator instances
- are allowed to abandon multiblock carriers. If <c>de</c> (default
- enabled) is passed instead of a <c><![CDATA[<utilization>]]></c>,
- a recomended non zero utilization value will be used. The actual
- value chosen depend on allocator type and may be changed between
- ERTS versions. Currently the default equals <c>de</c>, but this
- may be changed in the future. Carriers will be abandoned when
- memory utilization in the allocator instance falls below the
- utilization value used. Once a carrier has been abandoned, no new
- allocations will be made in it. When an allocator instance gets an
- increased multiblock carrier need, it will first try to fetch an
- abandoned carrier from an allocator instances of the same
- allocator type. If no abandoned carrier could be fetched, it will
- create a new empty carrier. When an abandoned carrier has been
- fetched it will function as an ordinary carrier. This feature has
- special requirements on the
- <seealso marker="#M_as">allocation strategy</seealso> used. Currently
- only the strategies <c>aoff</c>, <c>aoffcbf</c> and <c>aoffcaobf</c> support
- abandoned carriers. This feature also requires
- <seealso marker="#M_t">multiple thread specific instances</seealso>
- to be enabled. When enabling this feature, multiple thread specific
- instances will be enabled if not already enabled, and the
- <c>aoffcbf</c> strategy will be enabled if current strategy does not
- support abandoned carriers. This feature can be enabled on all
- allocators based on the <c>alloc_util</c> framework with the
- exception of <c>temp_alloc</c> (which would be pointless).
- </item>
- <tag><marker id="M_as"/><c><![CDATA[+M<S>as bf|aobf|aoff|aoffcbf|aoffcaobf|gf|af]]></c></tag>
- <item>
- Allocation strategy. Valid strategies are <c>bf</c> (best fit),
- <c>aobf</c> (address order best fit), <c>aoff</c> (address order first fit),
- <c>aoffcbf</c> (address order first fit carrier best fit),
- <c>aoffcaobf</c> (address order first fit carrier address order best fit),
- <c>gf</c> (good fit), and <c>af</c> (a fit). See
- <seealso marker="#strategy">the description of allocation strategies</seealso> in "the <c>alloc_util</c> framework" section.</item>
- <tag><marker id="M_asbcst"/><c><![CDATA[+M<S>asbcst <size>]]></c></tag>
- <item>
- Absolute singleblock carrier shrink threshold (in
- kilobytes). When a block located in an
- <c>mseg_alloc</c> singleblock carrier is shrunk, the carrier
- will be left unchanged if the amount of unused memory is less
- than this threshold; otherwise, the carrier will be shrunk.
- See also <seealso marker="#M_rsbcst">rsbcst</seealso>.</item>
- <tag><marker id="M_e"/><c><![CDATA[+M<S>e true|false]]></c></tag>
- <item>
- Enable allocator <c><![CDATA[<S>]]></c>.</item>
- <tag><marker id="M_lmbcs"/><c><![CDATA[+M<S>lmbcs <size>]]></c></tag>
- <item>
- Largest (<c>mseg_alloc</c>) multiblock carrier size (in
- kilobytes). See <seealso marker="#mseg_mbc_sizes">the description
- on how sizes for mseg_alloc multiblock carriers are decided</seealso>
- in "the <c>alloc_util</c> framework" section. On 32-bit Unix style OS
- this limit can not be set higher than 128 megabyte.</item>
- <tag><marker id="M_mbcgs"/><c><![CDATA[+M<S>mbcgs <ratio>]]></c></tag>
- <item>
- (<c>mseg_alloc</c>) multiblock carrier growth stages. See
- <seealso marker="#mseg_mbc_sizes">the description on how sizes for
- mseg_alloc multiblock carriers are decided</seealso>
- in "the <c>alloc_util</c> framework" section.</item>
- <tag><marker id="M_mbsd"/><c><![CDATA[+M<S>mbsd <depth>]]></c></tag>
- <item>
- Max block search depth. This flag has effect only if the
- good fit strategy has been selected for allocator
- <c><![CDATA[<S>]]></c>. When the good fit strategy is used, free
- blocks are placed in segregated free-lists. Each free list
- contains blocks of sizes in a specific range. The max block
- search depth sets a limit on the maximum number of blocks to
- inspect in a free list during a search for suitable block
- satisfying the request.</item>
- <tag><marker id="M_mmbcs"/><c><![CDATA[+M<S>mmbcs <size>]]></c></tag>
- <item>
- Main multiblock carrier size. Sets the size of the main
- multiblock carrier for allocator <c><![CDATA[<S>]]></c>. The main
- multiblock carrier is allocated via <c><![CDATA[sys_alloc]]></c> and is
- never deallocated.</item>
- <tag><marker id="M_mmmbc"/><c><![CDATA[+M<S>mmmbc <amount>]]></c></tag>
- <item>
- Max <c>mseg_alloc</c> multiblock carriers. Maximum number of
- multiblock carriers allocated via <c>mseg_alloc</c> by
- allocator <c><![CDATA[<S>]]></c>. When this limit has been reached,
- new multiblock carriers will be allocated via
- <c>sys_alloc</c>.</item>
- <tag><marker id="M_mmsbc"/><c><![CDATA[+M<S>mmsbc <amount>]]></c></tag>
- <item>
- Max <c>mseg_alloc</c> singleblock carriers. Maximum number of
- singleblock carriers allocated via <c>mseg_alloc</c> by
- allocator <c><![CDATA[<S>]]></c>. When this limit has been reached,
- new singleblock carriers will be allocated via
- <c>sys_alloc</c>.</item>
- <tag><marker id="M_ramv"/><c><![CDATA[+M<S>ramv <bool>]]></c></tag>
- <item>
- Realloc always moves. When enabled, reallocate operations will
- more or less be translated into an allocate, copy, free sequence.
- This often reduce memory fragmentation, but costs performance.
- </item>
- <tag><marker id="M_rmbcmt"/><c><![CDATA[+M<S>rmbcmt <ratio>]]></c></tag>
- <item>
- Relative multiblock carrier move threshold (in percent). When
- a block located in a multiblock carrier is shrunk,
- the block will be moved if the ratio of the size of the returned
- memory compared to the previous size is more than this threshold;
- otherwise, the block will be shrunk at current location.</item>
- <tag><marker id="M_rsbcmt"/><c><![CDATA[+M<S>rsbcmt <ratio>]]></c></tag>
- <item>
- Relative singleblock carrier move threshold (in percent). When
- a block located in a singleblock carrier is shrunk to
- a size smaller than the value of the
- <seealso marker="#M_sbct">sbct</seealso> parameter,
- the block will be left unchanged in the singleblock carrier if
- the ratio of unused memory is less than this threshold;
- otherwise, it will be moved into a multiblock carrier. </item>
- <tag><marker id="M_rsbcst"/><c><![CDATA[+M<S>rsbcst <ratio>]]></c></tag>
- <item>
- Relative singleblock carrier shrink threshold (in
- percent). When a block located in an <c>mseg_alloc</c>
- singleblock carrier is shrunk, the carrier will be left
- unchanged if the ratio of unused memory is less than this
- threshold; otherwise, the carrier will be shrunk.
- See also <seealso marker="#M_asbcst">asbcst</seealso>.</item>
- <tag><marker id="M_sbct"/><c><![CDATA[+M<S>sbct <size>]]></c></tag>
- <item>
- Singleblock carrier threshold. Blocks larger than this
- threshold will be placed in singleblock carriers. Blocks
- smaller than this threshold will be placed in multiblock
- carriers. On 32-bit Unix style OS this threshold can not be set higher
- than 8 megabytes.</item>
- <tag><marker id="M_smbcs"/><c><![CDATA[+M<S>smbcs <size>]]></c></tag>
- <item>
- Smallest (<c>mseg_alloc</c>) multiblock carrier size (in
- kilobytes). See <seealso marker="#mseg_mbc_sizes">the description
- on how sizes for mseg_alloc multiblock carriers are decided</seealso>
- in "the <c>alloc_util</c> framework" section.</item>
- <tag><marker id="M_t"/><c><![CDATA[+M<S>t true|false]]></c></tag>
- <item>
- <p>Multiple, thread specific instances of the allocator.
- This option will only have any effect on the runtime system
- with SMP support. Default behaviour on the runtime system with
- SMP support is <c>NoSchedulers+1</c> instances. Each scheduler will use
- a lock-free instance of its own and other threads will use
- a common instance.</p>
- <p>It was previously (before ERTS version 5.9) possible to configure
- a smaller amount of thread specific instances than schedulers.
- This is, however, not possible any more.</p>
- </item>
- </taglist>
- <p>Currently the following flags are available for configuration of
- <c>alloc_util</c>, i.e. all allocators based on <c>alloc_util</c>
- will be effected:</p>
- <taglist>
- <tag><marker id="Muycs"/><c><![CDATA[+Muycs <size>]]></c></tag>
- <item>
- <c>sys_alloc</c> carrier size. Carriers allocated via
- <c>sys_alloc</c> will be allocated in sizes which are
- multiples of the <c>sys_alloc</c> carrier size. This is not
- true for main multiblock carriers and carriers allocated
- during a memory shortage, though.</item>
- <tag><marker id="Mummc"/><c><![CDATA[+Mummc <amount>]]></c></tag>
- <item>
- Max <c>mseg_alloc</c> carriers. Maximum number of carriers
- placed in separate memory segments. When this limit has been
- reached, new carriers will be placed in memory retrieved from
- <c>sys_alloc</c>.</item>
- <tag><marker id="Musac"/><c><![CDATA[+Musac <bool>]]></c></tag>
- <item>
- Allow <c>sys_alloc</c> carriers. By default <c>true</c>. If
- set to <c>false</c>, <c>sys_alloc</c> carriers will never be
- created by allocators using the <c>alloc_util</c> framework.</item>
- </taglist>
- <p>The following flag is special for <c>literal_alloc</c>:</p>
- <taglist>
- <tag><marker id="MIscs"/><c><![CDATA[+MIscs <size in MB>]]></c></tag>
- <item>
- <c>literal_alloc</c> super carrier size (in MB). The amount of
- <em>virtual</em> address space reserved for literal terms in
- Erlang code on 64-bit architectures. The default is 1024 (1GB)
- and is usually sufficient. The flag is ignored on 32-bit
- architectures.</item>
- </taglist>
- <p>The following flag is special for <c>exec_alloc</c>:</p>
- <taglist>
- <tag><marker id="MXscs"/><c><![CDATA[+MXscs <size in MB>]]></c></tag>
- <item>
- <c>exec_alloc</c> super carrier size (in MB). The amount of
- <em>virtual</em> address space reserved for native executable code
- used by hipe on specific architectures (x86_64). The default is 512 MB.
- </item>
- </taglist>
- <p>Instrumentation flags:</p>
- <taglist>
- <tag><marker id="Mim"/><c>+Mim true|false</c></tag>
- <item>
- A map over current allocations is kept by the emulator. The
- allocation map can be retrieved via the <c>instrument</c>
- module. <c>+Mim true</c> implies <c>+Mis true</c>.
- <c>+Mim true</c> is the same as
- <seealso marker="erl#instr">-instr</seealso>.</item>
- <tag><marker id="Mis"/><c>+Mis true|false</c></tag>
- <item>
- Status over allocated memory is kept by the emulator. The
- allocation status can be retrieved via the <c>instrument</c>
- module.</item>
- <tag><marker id="Mit"/><c>+Mit X</c></tag>
- <item>
- Reserved for future use. Do <em>not</em> use this flag.</item>
- </taglist>
- <note>
- <p>When instrumentation of the emulator is enabled, the emulator
- uses more memory and runs slower.</p>
- </note>
- <p>Other flags:</p>
- <taglist>
- <tag><marker id="Mea"/><c>+Mea min|max|r9c|r10b|r11b|config</c></tag>
- <item>
+
+ <section>
+ <title>Flags for Configuration of mseg_alloc</title>
+ <taglist>
+ <tag><marker id="MMamcbf"/><c><![CDATA[+MMamcbf <size>]]></c></tag>
+ <item>
+ <p>Absolute maximum cache bad fit (in kilobytes). A segment in the
+ memory segment cache is not reused if its size exceeds the
+ requested size with more than the value of this
+ parameter. Defaults to <c>4096</c>.</p>
+ </item>
+ <tag><marker id="MMrmcbf"/><c><![CDATA[+MMrmcbf <ratio>]]></c></tag>
+ <item>
+ <p>Relative maximum cache bad fit (in percent). A segment in the
+ memory segment cache is not reused if its size exceeds the
+ requested size with more than relative maximum cache bad fit
+ percent of the requested size. Defaults to <c>20</c>.</p>
+ </item>
+ <tag><marker id="MMsco"/><c><![CDATA[+MMsco true|false]]></c></tag>
+ <item>
+ <p>Sets <seealso marker="#MMscs">super carrier</seealso> only flag.
+ Defaults to <c>true</c>. When a super carrier is used and this
+ flag is <c>true</c>, <c>mseg_alloc</c> only creates carriers in
+ the super carrier. Notice that the <c>alloc_util</c> framework can
+ create <c>sys_alloc</c> carriers, so if you want all carriers to
+ be created in the super carrier, you therefore want to disable use
+ of <c>sys_alloc</c> carriers by also passing
+ <seealso marker="#Musac"><c>+Musac false</c></seealso>. When
+ the flag is <c>false</c>, <c>mseg_alloc</c> tries to create carriers
+ outside of the super carrier when the super carrier is full.</p>
+ <note>
+ <p>Setting this flag to <c>false</c> is possibly not supported
+ on all systems. The flag is then ignored.</p>
+ </note>
+ <note>
+ <p>The super carrier cannot be enabled or
+ disabled on halfword heap systems. This flag is
+ ignored on halfword heap systems.</p>
+ </note>
+ </item>
+ <tag><marker id="MMscrfsd"/><c><![CDATA[+MMscrfsd <amount>]]></c></tag>
+ <item>
+ <p>Sets <seealso marker="#MMscs">super carrier</seealso> reserved
+ free segment descriptors. Defaults to <c>65536</c>.
+ This parameter determines the amount of memory to reserve for
+ free segment descriptors used by the super carrier. If the system
+ runs out of reserved memory for free segment descriptors, other
+ memory is used. This can however cause fragmentation issues,
+ so you want to ensure that this never happens. The maximum amount
+ of free segment descriptors used can be retrieved from the
+ <c>erts_mmap</c> tuple part of the result from calling
+ <seealso marker="erts:erlang#system_info_allocator_tuple">
+ <c>erlang:system_info({allocator, mseg_alloc})</c></seealso>.</p>
+ </item>
+ <tag><marker id="MMscrpm"/><c><![CDATA[+MMscrpm true|false]]></c></tag>
+ <item>
+ <p>Sets <seealso marker="#MMscs">super carrier</seealso> reserve
+ physical memory flag. Defaults to <c>true</c>. When this flag is
+ <c>true</c>, physical memory is reserved for the whole super
+ carrier at once when it is created. The reservation is after that
+ left unchanged. When this flag is set to <c>false</c>, only virtual
+ address space is reserved for the super carrier upon creation.
+ The system attempts to reserve physical memory upon carrier
+ creations in the super carrier, and attempt to unreserve physical
+ memory upon carrier destructions in the super carrier.</p>
+ <note>
+ <p>What reservation of physical memory means, highly
+ depends on the operating system, and how it is configured. For
+ example, different memory overcommit settings on Linux drastically
+ change the behavior.</p>
+ <p>Setting this flag to <c>false</c> is possibly not supported on
+ all systems. The flag is then ignored.</p>
+ </note>
+ <note>
+ <p>The super carrier cannot be enabled or
+ disabled on halfword heap systems. This flag is
+ ignored on halfword heap systems.</p>
+ </note>
+ </item>
+ <tag><marker id="MMscs"/><c><![CDATA[+MMscs <size in MB>]]></c></tag>
+ <item>
+ <p>Sets super carrier size (in MB). Defaults to <c>0</c>, that is,
+ the super carrier is by default disabled. The super
+ carrier is a large continuous area in the virtual address space.
+ <c>mseg_alloc</c> always tries to create new carriers in the super
+ carrier if it exists. Notice that the <c>alloc_util</c> framework
+ can create <c>sys_alloc</c> carriers. For more information, see
+ <seealso marker="#MMsco"><c>+MMsco</c></seealso>.</p>
+ <note>
+ <p>The super carrier cannot be enabled or
+ disabled on halfword heap systems. This flag is
+ ignored on halfword heap systems.</p>
+ </note>
+ </item>
+ <tag><marker id="MMmcs"/><c><![CDATA[+MMmcs <amount>]]></c></tag>
+ <item>
+ <p>Maximum cached segments. The maximum number of memory segments
+ stored in the memory segment cache. Valid range is <c>[0, 30]</c>.
+ Defaults to <c>10</c>.</p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Flags for Configuration of sys_alloc</title>
+ <taglist>
+ <tag><marker id="MYe"/><c>+MYe true</c></tag>
+ <item>
+ <p>Enables <c>sys_alloc</c>.</p>
+ <note>
+ <p><c>sys_alloc</c> cannot be disabled.</p>
+ </note>
+ </item>
+ <tag><marker id="MYm"/><c>+MYm libc</c></tag>
+ <item>
+ <p><c>malloc</c> library to use. Only
+ <c>libc</c> is available. <c>libc</c> enables the standard
+ <c>libc</c> <c>malloc</c> implementation. By default <c>libc</c>
+ is used.</p>
+ </item>
+ <tag><marker id="MYtt"/><c><![CDATA[+MYtt <size>]]></c></tag>
+ <item>
+ <p>Trim threshold size (in kilobytes). This is the maximum amount
+ of free memory at the top of the heap (allocated by
+ <c>sbrk</c>) that is kept by <c>malloc</c> (not
+ released to the operating system). When the amount of free
+ memory at the top of the heap exceeds the trim threshold,
+ <c>malloc</c> releases it (by calling <c>sbrk</c>).
+ Trim threshold is specified in kilobytes.
+ Defaults to <c>128</c>.</p>
+ <note>
+ <p>This flag has effect only when the emulator is linked with
+ the GNU C library, and uses its <c>malloc</c> implementation.</p>
+ </note>
+ </item>
+ <tag><marker id="MYtp"/><c><![CDATA[+MYtp <size>]]></c></tag>
+ <item>
+ <p>Top pad size (in kilobytes). This is the amount of extra
+ memory that is allocated by <c>malloc</c> when
+ <c>sbrk</c> is called to get more memory from the operating
+ system. Defaults to <c>0</c>.</p>
+ <note>
+ <p>This flag has effect only when the emulator is linked with
+ the GNU C library, and uses its <c>malloc</c> implementation.</p>
+ </note>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Flags for Configuration of Allocators Based on alloc_util</title>
+ <p>If <c>u</c> is used as subsystem identifier (that is,
+ <c><![CDATA[<S> = u]]></c>), all allocators based on
+ <c>alloc_util</c> are effected. If <c>B</c>, <c>D</c>, <c>E</c>,
+ <c>F</c>, <c>H</c>, <c>L</c>, <c>R</c>, <c>S</c>, or <c>T</c> is used
+ as subsystem identifier, only the specific allocator identifier is
+ effected.</p>
+
+ <taglist>
+ <tag><marker id="M_acul"/><c><![CDATA[+M<S>acul <utilization>|de]]></c>
+ </tag>
+ <item>
+ <p>Abandon carrier utilization limit. A valid
+ <c><![CDATA[<utilization>]]></c> is an integer in the range
+ <c>[0, 100]</c> representing utilization in percent. When a
+ utilization value &gt; 0 is used, allocator instances
+ are allowed to abandon multiblock carriers. If <c>de</c> (default
+ enabled) is passed instead of a <c><![CDATA[<utilization>]]></c>,
+ a recomended non-zero utilization value is used. The value
+ chosen depends on the allocator type and can be changed between
+ <c>ERTS</c> versions. Defaults to <c>de</c>, but this
+ can be changed in the future.</p>
+ <p>Carriers are abandoned when
+ memory utilization in the allocator instance falls below the
+ utilization value used. Once a carrier is abandoned, no new
+ allocations are made in it. When an allocator instance gets an
+ increased multiblock carrier need, it first tries to fetch an
+ abandoned carrier from an allocator instances of the same
+ allocator type. If no abandoned carrier can be fetched, it
+ creates a new empty carrier. When an abandoned carrier has been
+ fetched, it will function as an ordinary carrier. This feature has
+ special requirements on the
+ <seealso marker="#M_as">allocation strategy</seealso> used. Only
+ the strategies <c>aoff</c>, <c>aoffcbf</c>, and <c>aoffcaobf</c>
+ support abandoned carriers.</p>
+ <p>This feature also requires
+ <seealso marker="#M_t">multiple thread specific instances</seealso>
+ to be enabled. When enabling this feature, multiple thread-specific
+ instances are enabled if not already enabled, and the
+ <c>aoffcbf</c> strategy is enabled if the current strategy does not
+ support abandoned carriers. This feature can be enabled on all
+ allocators based on the <c>alloc_util</c> framework, except
+ <c>temp_alloc</c> (which would be pointless).</p>
+ </item>
+ <tag><marker id="M_as"/>
+ <c><![CDATA[+M<S>as bf|aobf|aoff|aoffcbf|aoffcaobf|gf|af]]></c></tag>
+ <item>
+ <p>Allocation strategy. The following strategies are valid:</p>
+ <list type="bulleted">
+ <item><c>bf</c> (best fit)</item>
+ <item><c>aobf</c> (address order best fit)</item>
+ <item><c>aoff</c> (address order first fit)</item>
+ <item><c>aoffcbf</c> (address order first fit carrier best fit)
+ </item>
+ <item><c>aoffcaobf</c> (address order first fit carrier address
+ order best fit)</item>
+ <item><c>gf</c> (good fit)</item>
+ <item><c>af</c> (a fit)</item>
+ </list>
+ <p>See the description of allocation strategies in section
+ <seealso marker="#strategy">The alloc_util Framework</seealso>.</p>
+ </item>
+ <tag><marker id="M_asbcst"/><c><![CDATA[+M<S>asbcst <size>]]></c></tag>
+ <item>
+ <p>Absolute singleblock carrier shrink threshold (in
+ kilobytes). When a block located in an
+ <c>mseg_alloc</c> singleblock carrier is shrunk, the carrier
+ is left unchanged if the amount of unused memory is less
+ than this threshold, otherwise the carrier is shrunk.
+ See also <seealso marker="#M_rsbcst"><c>rsbcst</c></seealso>.</p>
+ </item>
+ <tag><marker id="M_e"/><c><![CDATA[+M<S>e true|false]]></c></tag>
+ <item>
+ <p>Enables allocator <c><![CDATA[<S>]]></c>.</p>
+ </item>
+ <tag><marker id="M_lmbcs"/><c><![CDATA[+M<S>lmbcs <size>]]></c></tag>
+ <item>
+ <p>Largest (<c>mseg_alloc</c>) multiblock carrier size (in kilobytes).
+ See the description on how sizes for <c>mseg_alloc</c> multiblock
+ carriers are decided in section
+ <seealso marker="#mseg_mbc_sizes">
+ The alloc_util Framework</seealso>. On
+ 32-bit Unix style OS this limit cannot be set &gt; 128 MB.</p>
+ </item>
+ <tag><marker id="M_mbcgs"/><c><![CDATA[+M<S>mbcgs <ratio>]]></c></tag>
+ <item>
+ <p>(<c>mseg_alloc</c>) multiblock carrier growth stages.
+ See the description on how sizes for <c>mseg_alloc</c> multiblock
+ carriers are decided in section
+ <seealso marker="#mseg_mbc_sizes">
+ The alloc_util Framework</seealso>.</p>
+ </item>
+ <tag><marker id="M_mbsd"/><c><![CDATA[+M<S>mbsd <depth>]]></c></tag>
+ <item>
+ <p>Maximum block search depth. This flag has effect only if the
+ good fit strategy is selected for allocator
+ <c><![CDATA[<S>]]></c>. When the good fit strategy is used, free
+ blocks are placed in segregated free-lists. Each free-list
+ contains blocks of sizes in a specific range. The maxiumum block
+ search depth sets a limit on the maximum number of blocks to
+ inspect in a free-list during a search for suitable block
+ satisfying the request.</p>
+ </item>
+ <tag><marker id="M_mmbcs"/><c><![CDATA[+M<S>mmbcs <size>]]></c></tag>
+ <item>
+ <p>Main multiblock carrier size. Sets the size of the main
+ multiblock carrier for allocator <c><![CDATA[<S>]]></c>. The main
+ multiblock carrier is allocated through <c><![CDATA[sys_alloc]]></c>
+ and is never deallocated.</p>
+ </item>
+ <tag><marker id="M_mmmbc"/><c><![CDATA[+M<S>mmmbc <amount>]]></c></tag>
+ <item>
+ <p>Maximum <c>mseg_alloc</c> multiblock carriers. Maximum number of
+ multiblock carriers allocated through <c>mseg_alloc</c> by
+ allocator <c><![CDATA[<S>]]></c>. When this limit is reached,
+ new multiblock carriers are allocated through
+ <c>sys_alloc</c>.</p>
+ </item>
+ <tag><marker id="M_mmsbc"/><c><![CDATA[+M<S>mmsbc <amount>]]></c></tag>
+ <item>
+ <p>Maximum <c>mseg_alloc</c> singleblock carriers. Maximum number of
+ singleblock carriers allocated through <c>mseg_alloc</c> by
+ allocator <c><![CDATA[<S>]]></c>. When this limit is reached,
+ new singleblock carriers are allocated through
+ <c>sys_alloc</c>.</p>
+ </item>
+ <tag><marker id="M_ramv"/><c><![CDATA[+M<S>ramv <bool>]]></c></tag>
+ <item>
+ <p>Realloc always moves. When enabled, reallocate operations are
+ more or less translated into an allocate, copy, free sequence.
+ This often reduces memory fragmentation, but costs performance.</p>
+ </item>
+ <tag><marker id="M_rmbcmt"/><c><![CDATA[+M<S>rmbcmt <ratio>]]></c></tag>
+ <item>
+ <p>Relative multiblock carrier move threshold (in percent). When
+ a block located in a multiblock carrier is shrunk,
+ the block is moved if the ratio of the size of the returned
+ memory compared to the previous size is more than this threshold,
+ otherwise the block is shrunk at the current location.</p>
+ </item>
+ <tag><marker id="M_rsbcmt"/><c><![CDATA[+M<S>rsbcmt <ratio>]]></c></tag>
+ <item>
+ <p>Relative singleblock carrier move threshold (in percent). When
+ a block located in a singleblock carrier is shrunk to
+ a size smaller than the value of parameter
+ <seealso marker="#M_sbct"><c>sbct</c></seealso>,
+ the block is left unchanged in the singleblock carrier if
+ the ratio of unused memory is less than this threshold,
+ otherwise it is moved into a multiblock carrier.</p>
+ </item>
+ <tag><marker id="M_rsbcst"/><c><![CDATA[+M<S>rsbcst <ratio>]]></c></tag>
+ <item>
+ <p>Relative singleblock carrier shrink threshold (in
+ percent). When a block located in an <c>mseg_alloc</c>
+ singleblock carrier is shrunk, the carrier is left
+ unchanged if the ratio of unused memory is less than this
+ threshold, otherwise the carrier is shrunk.
+ See also <seealso marker="#M_asbcst"><c>asbcst</c></seealso>.</p>
+ </item>
+ <tag><marker id="M_sbct"/><c><![CDATA[+M<S>sbct <size>]]></c></tag>
+ <item>
+ <p>Singleblock carrier threshold. Blocks larger than this
+ threshold are placed in singleblock carriers. Blocks
+ smaller than this threshold are placed in multiblock
+ carriers. On 32-bit Unix style OS this threshold cannot be set
+ &gt; 8 MB.</p>
+ </item>
+ <tag><marker id="M_smbcs"/><c><![CDATA[+M<S>smbcs <size>]]></c></tag>
+ <item>
+ <p>Smallest (<c>mseg_alloc</c>) multiblock carrier size (in
+ kilobytes). See the description on how sizes for <c>mseg_alloc</c>
+ multiblock carriers are decided in section
+ <seealso marker="#mseg_mbc_sizes">
+ The alloc_util Framework</seealso>.</p>
+ </item>
+ <tag><marker id="M_t"/><c><![CDATA[+M<S>t true|false]]></c></tag>
+ <item>
+ <p>Multiple, thread-specific instances of the allocator.
+ This option has only effect on the runtime system
+ with SMP support. Default behavior on the runtime system with
+ SMP support is <c>NoSchedulers+1</c> instances. Each scheduler
+ uses a lock-free instance of its own and other threads use
+ a common instance.</p>
+ <p>Before <c>ERTS</c> 5.9 it was possible to configure
+ a smaller number of thread-specific instances than schedulers.
+ This is, however, not possible anymore.</p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Flags for Configuration of alloc_util</title>
+ <p>All allocators based on <c>alloc_util</c> are effected.</p>
+
+ <taglist>
+ <tag><marker id="Muycs"/><c><![CDATA[+Muycs <size>]]></c></tag>
+ <item>
+ <p><c>sys_alloc</c> carrier size. Carriers allocated through
+ <c>sys_alloc</c> are allocated in sizes that are
+ multiples of the <c>sys_alloc</c> carrier size. This is not
+ true for main multiblock carriers and carriers allocated
+ during a memory shortage, though.</p>
+ </item>
+ <tag><marker id="Mummc"/><c><![CDATA[+Mummc <amount>]]></c></tag>
+ <item>
+ <p>Maximum <c>mseg_alloc</c> carriers. Maximum number of carriers
+ placed in separate memory segments. When this limit is
+ reached, new carriers are placed in memory retrieved from
+ <c>sys_alloc</c>.</p>
+ </item>
+ <tag><marker id="Musac"/><c><![CDATA[+Musac <bool>]]></c></tag>
+ <item>
+ <p>Allow <c>sys_alloc</c> carriers. Defaults to <c>true</c>.
+ If set to <c>false</c>, <c>sys_alloc</c> carriers are never
+ created by allocators using the <c>alloc_util</c> framework.</p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Special Flag for literal_alloc</title>
<taglist>
- <tag><c>min</c></tag>
+ <tag><marker id="MIscs"/><c><![CDATA[+MIscs <size in MB>]]></c></tag>
<item>
- Disables all allocators that can be disabled.
- </item>
+ <p><c>literal_alloc</c> super carrier size (in MB). The amount of
+ <em>virtual</em> address space reserved for literal terms in
+ Erlang code on 64-bit architectures. Defaults to <c>1024</c>
+ (that is, 1 GB), which is usually sufficient.
+ The flag is ignored on 32-bit architectures.</p>
+ </item>
+ </taglist>
+ </section>
- <tag><c>max</c></tag>
+ <section>
+ <title>Special Flag for exec_alloc</title>
+ <taglist>
+ <tag><marker id="MXscs"/><c><![CDATA[+MXscs <size in MB>]]></c></tag>
<item>
- Enables all allocators (currently default).
- </item>
+ <p><c>exec_alloc</c> super carrier size (in MB). The amount of
+ <em>virtual</em> address space reserved for native executable code
+ used by the <seealso marker="hipe"><c>HiPE</c></seealso> application
+ on specific architectures (x86_64). Defaults to <c>512</c>.</p>
+ </item>
+ </taglist>
+ </section>
- <tag><c>r9c|r10b|r11b</c></tag>
+ <section>
+ <title>Instrumentation Flags</title>
+ <taglist>
+ <tag><marker id="Mim"/><c>+Mim true|false</c></tag>
<item>
- Configures all allocators as they were configured in respective
- OTP release. These will eventually be removed.
- </item>
+ <p>A map over current allocations is kept by the emulator.
+ The allocation map can be retrieved through module
+ <seealso marker="tools:instrument">
+ <c>tools:instrument(3)</c></seealso>. <c>+Mim true</c>
+ implies <c>+Mis true</c>. <c>+Mim true</c> is the same as flag
+ <seealso marker="erl#instr"><c>-instr</c></seealso> in
+ <c>erl(1)</c>.</p>
+ </item>
+ <tag><marker id="Mis"/><c>+Mis true|false</c></tag>
+ <item>
+ <p>Status over allocated memory is kept by the emulator.
+ The allocation status can be retrieved through module
+ <seealso marker="tools:instrument">
+ <c>tools:instrument(3)</c></seealso>.</p>
+ </item>
+ <tag><marker id="Mit"/><c>+Mit X</c></tag>
+ <item>
+ <p>Reserved for future use. Do <em>not</em> use this flag.</p>
+ </item>
+ </taglist>
- <tag><c>config</c></tag>
+ <note>
+ <p>When instrumentation of the emulator is enabled, the emulator
+ uses more memory and runs slower.</p>
+ </note>
+ </section>
+
+ <section>
+ <title>Other Flags</title>
+ <taglist>
+ <tag><marker id="Mea"/><c>+Mea min|max|r9c|r10b|r11b|config</c></tag>
+ <item>
+ <p>Options:</p>
+ <taglist>
+ <tag><c>min</c></tag>
+ <item>
+ <p>Disables all allocators that can be disabled.</p>
+ </item>
+ <tag><c>max</c></tag>
+ <item>
+ <p>Enables all allocators (default).</p>
+ </item>
+ <tag><c>r9c|r10b|r11b</c></tag>
+ <item>
+ <p>Configures all allocators as they were configured in respective
+ Erlang/OTP release. These will eventually be removed.</p>
+ </item>
+ <tag><c>config</c></tag>
+ <item>
+ <p>Disables features that cannot be enabled while creating an
+ allocator configuration with
+ <seealso marker="runtime_tools:erts_alloc_config">
+ <c>runtime_tools:erts_alloc_config(3)</c></seealso>.</p>
+ <note>
+ <p>This option is to be used only while running
+ <c>runtime_tools:erts_alloc_config(3)</c>, <em>not</em> when
+ using the created configuration.</p>
+ </note>
+ </item>
+ </taglist>
+ </item>
+ <tag><marker id="Mlpm"/><c>+Mlpm all|no</c></tag>
<item>
- Disables features that cannot be enabled while creating an
- allocator configuration with
- <seealso marker="runtime_tools:erts_alloc_config">erts_alloc_config(3)</seealso>.
- Note, this option should only be used while running
- <c>erts_alloc_config</c>, <em>not</em> when using the created
- configuration.
+ <p>Lock physical memory. Defaults to <c>no</c>, that is,
+ no physical memory is locked. If set to <c>all</c>, all
+ memory mappings made by the runtime system are locked into
+ physical memory. If set to <c>all</c>, the runtime system fails to
+ start if this feature is not supported, the user has not got enough
+ privileges, or the user is not allowed to lock enough physical
+ memory. The runtime system also fails with an out of memory
+ condition if the user limit on the amount of locked memory is
+ reached.</p>
</item>
</taglist>
- </item>
- <tag><marker id="Mlpm"/><c>+Mlpm all|no</c></tag>
- <item>Lock physical memory. The default value is <c>no</c>, i.e.,
- no physical memory will be locked. If set to <c>all</c>, all
- memory mappings made by the runtime system, will be locked into
- physical memory. If set to <c>all</c>, the runtime system will fail
- to start if this feature is not supported, the user has not got enough
- privileges, or the user is not allowed to lock enough physical memory.
- The runtime system will also fail with an out of memory condition
- if the user limit on the amount of locked memory is reached.
- </item>
- </taglist>
- <p>Only some default values have been presented
- here.
- <seealso marker="erts:erlang#system_info_allocator">erlang:system_info(allocator)</seealso>,
- and
- <seealso marker="erts:erlang#system_info_allocator_tuple">erlang:system_info({allocator, Alloc})</seealso>
- can be used in order to obtain currently used settings and current
- status of the allocators.</p>
+ </section>
+ </section>
+
+ <section>
+ <title>Notes</title>
+ <p>Only some default values have been presented here. For information
+ about the currently used settings and the current status of the
+ allocators, see
+ <seealso marker="erts:erlang#system_info_allocator">
+ <c>erlang:system_info(allocator)</c></seealso> and
+ <seealso marker="erts:erlang#system_info_allocator_tuple">
+ <c>erlang:system_info({allocator, Alloc})</c></seealso>.</p>
+
<note>
- <p>Most of these flags are highly implementation dependent, and they
- may be changed or removed without prior notice.</p>
+ <p>Most of these flags are highly implementation-dependent and
+ can be changed or removed without prior notice.</p>
<p><c>erts_alloc</c> is not obliged to strictly use the settings that
- have been passed to it (it may even ignore them).</p>
+ have been passed to it (it can even ignore them).</p>
</note>
- <p><seealso marker="runtime_tools:erts_alloc_config">erts_alloc_config(3)</seealso>
- is a tool that can be used to aid creation of an
+
+ <p>The <seealso marker="runtime_tools:erts_alloc_config">
+ <c>runtime_tools:erts_alloc_config(3)</c></seealso>
+ tool can be used to aid creation of an
<c>erts_alloc</c> configuration that is suitable for a limited
number of runtime scenarios.</p>
</section>
<section>
- <title>SEE ALSO</title>
- <p><seealso marker="runtime_tools:erts_alloc_config">erts_alloc_config(3)</seealso>,
- <seealso marker="erl">erl(1)</seealso>,
- <seealso marker="tools:instrument">instrument(3)</seealso>,
- <seealso marker="erts:erlang">erlang(3)</seealso></p>
+ <title>See Also</title>
+ <p><seealso marker="erl"><c>erl(1)</c></seealso>,
+ <seealso marker="erlang"><c>erlang(3)</c></seealso>,
+ <seealso marker="runtime_tools:erts_alloc_config">
+ <c>runtime_tools:erts_alloc_config(3)</c></seealso>,
+ <seealso marker="tools:instrument">
+ <c>tools:instrument(3)</c></seealso></p>
</section>
</cref>