diff options
Diffstat (limited to 'erts/doc/src/erts_alloc.xml')
| -rw-r--r-- | erts/doc/src/erts_alloc.xml | 78 |
1 files changed, 37 insertions, 41 deletions
diff --git a/erts/doc/src/erts_alloc.xml b/erts/doc/src/erts_alloc.xml index 452e5d990e..3b5ee5391c 100644 --- a/erts/doc/src/erts_alloc.xml +++ b/erts/doc/src/erts_alloc.xml @@ -4,7 +4,7 @@ <cref> <header> <copyright> - <year>2002</year><year>2010</year> + <year>2002</year><year>2011</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -58,11 +58,8 @@ <item>Allocator used for memory blocks that are expected to be long-lived, for example Erlang code.</item> <tag><c>fix_alloc</c></tag> - <item>A very fast allocator used for some fix-sized - data. <c>fix_alloc</c> manages a set of memory pools from - which memory blocks are handed out. <c>fix_alloc</c> - allocates memory pools from <c>ll_alloc</c>. Memory pools - that have been allocated are never deallocated.</item> + <item>A fast allocator used for some frequently used + fixed size data types.</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> @@ -83,7 +80,7 @@ where only small blocks are placed. Currently this allocator is disabled by default.</item> </taglist> - <p><c>sys_alloc</c> and <c>fix_alloc</c> are always enabled and + <p><c>sys_alloc</c> is always enabled and cannot be disabled. <c>mseg_alloc</c> is always enabled if it is available and an allocator that uses it is enabled. All other allocators can be <seealso marker="#M_e">enabled or disabled</seealso>. @@ -104,7 +101,7 @@ <marker id="alloc_util"></marker> <title>The alloc_util framework</title> <p>Internally a framework called <c>alloc_util</c> is used for - implementing allocators. <c>sys_alloc</c>, <c>fix_alloc</c>, and + implementing allocators. <c>sys_alloc</c>, and <c>mseg_alloc</c> do not use this framework; hence, the following does <em>not</em> apply to them.</p> <p>An allocator manages multiple areas, called carriers, in which @@ -126,9 +123,8 @@ 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> - <p> <marker id="mseg_mbc_sizes"></marker> - - Sizes of multiblock carriers allocated via <c>mseg_alloc</c> are + <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>), @@ -157,9 +153,8 @@ <p>Coalescing of free blocks are always performed immediately. 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 + <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> <taglist> @@ -180,6 +175,14 @@ used. The time complexity is proportional to log N, where N is the number of free blocks.</p> </item> + <tag>Address order first fit</tag> + <item> + <p>Strategy: Find the block with the lowest address that satisfies the + requested block size.</p> + <p>Implementation: A balanced binary search tree is + used. The time complexity is proportional to log N, where + N is the number of free blocks.</p> + </item> <tag>Good fit</tag> <item> <p>Strategy: Try to find the best fit, but settle for the best fit @@ -206,6 +209,14 @@ This since it will only cause 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 there are available + pre-allocated memory, 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> </section> <note><p> @@ -266,18 +277,6 @@ Max cached segments. The maximum number of memory segments stored in the memory segment cache. Valid range is 0-30. Default value is 5.</item> - <tag><marker id="MMcci"><c><![CDATA[+MMcci <time>]]></c></marker></tag> - <item> - Cache check interval (in milliseconds). The memory segment - cache is checked for segments to destroy at an interval - determined by this parameter. Default value is 1000.</item> - </taglist> - <p>The following flags are available for configuration of - <c>fix_alloc</c>:</p> - <taglist> - <tag><marker id="MFe"><c>+MFe true</c></marker></tag> - <item> - Enable <c>fix_alloc</c>. Note: <c>fix_alloc</c> cannot be disabled.</item> </taglist> <p>The following flags are available for configuration of <c>sys_alloc</c>:</p> @@ -316,15 +315,15 @@ 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>H</c>, <c>L</c>, <c>R</c>, <c>S</c>, or <c>T</c> is used as + <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_as"><c><![CDATA[+M<S>as bf|aobf|gf|af]]></c></marker></tag> + <tag><marker id="M_as"><c><![CDATA[+M<S>as bf|aobf|aoff|gf|af]]></c></marker></tag> <item> Allocation strategy. Valid strategies are <c>bf</c> (best fit), - <c>aobf</c> (address order best fit), <c>gf</c> (good fit), - and <c>af</c> (a fit). See + <c>aobf</c> (address order best fit), <c>aoff</c> (address order first 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></marker></tag> <item> @@ -435,26 +434,23 @@ 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|<amount>]]></c></marker></tag> + <tag><marker id="M_t"><c><![CDATA[+M<S>t true|false]]></c></marker></tag> <item> 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 (<c>N</c> equals the number of scheduler threads): + SMP support: <taglist> - <tag><c>temp_alloc</c></tag> - <item><c>N + 1</c> instances.</item> <tag><c>ll_alloc</c></tag> <item><c>1</c> instance.</item> <tag>Other allocators</tag> - <item><c>N</c> instances when <c>N</c> is less than or equal to - <c>16</c>. <c>16</c> instances when <c>N</c> is greater than - <c>16</c>.</item> + <item><c>NoSchedulers+1</c> instances. Each scheduler will use + a lock-free instance of its own and other threads will use + a common instance.</item> </taglist> - <c>temp_alloc</c> will always use <c>N + 1</c> instances when - this option has been enabled regardless of the amount passed. - Other allocators will use the same amount of instances as the - amount passed as long as it isn't greater than <c>N</c>. + 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. </item> </taglist> <p>Currently the following flags are available for configuration of |