diff options
Diffstat (limited to 'erts/doc/src/erts_alloc.xml')
| -rw-r--r-- | erts/doc/src/erts_alloc.xml | 94 |
1 files changed, 67 insertions, 27 deletions
diff --git a/erts/doc/src/erts_alloc.xml b/erts/doc/src/erts_alloc.xml index 51a4a2bca0..86e1e5168a 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> @@ -78,14 +78,20 @@ 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> + <tag><c>sbmbc_alloc</c></tag> + <item>Allocator used by other allocators for allocation of carriers + 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 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>. By default all allocators are enabled. - When an allocator is disabled, <c>sys_alloc</c> - is used instead of the disabled allocator.</p> + When an allocator is disabled, <c>sys_alloc</c> is used instead of + the disabled allocator. <c>sbmbc_alloc</c> is an exception. If + <c>sbmbc_alloc</c> is disabled, other allocators will not handle + small blocks in separate carriers.</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 @@ -103,21 +109,25 @@ 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 + separate memory segment (allocated via <c>mseg_alloc</c>), in + the heap segment (allocated via <c>sys_alloc</c>), or inside + another carrier (in case it is a carrier created by + <c>sbmbc_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 smaller than the value of the - <c>sbct</c> parameter are placed in multiblock - carriers. Normally an allocator creates a "main multiblock + in singleblock carriers. Blocks that are smaller than the value + of the <c>sbct</c> parameter are placed in multiblock + carriers. Blocks that are smaller than the small block multiblock + carrier threshold (<seealso marker="#M_sbmbct">sbmbct</seealso>) + will be placed in multiblock carriers only used for small blocks. + 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> - <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>), @@ -133,8 +143,11 @@ <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 to whole pages.</p> + <c>lmbcs</c> parameter, though. The size of multiblock carriers + for small blocks is determined by the small block multiblock + carrier size (<seealso marker="#M_sbmbcs">sbmbcs</seealso>). + Singleblock carriers allocated via <c>mseg_alloc</c> are sized + to whole pages.</p> <p>Sizes of carriers allocated via <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 @@ -143,9 +156,8 @@ <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> @@ -166,6 +178,14 @@ 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 @@ -194,6 +214,11 @@ </taglist> </section> + <note><p> + Currently only allocators using the best fit and the address order + best fit strategies are able to use "small block multi block carriers". + </p></note> + <section> <marker id="flags"></marker> <title>System Flags Effecting erts_alloc</title> @@ -215,6 +240,7 @@ the currently present allocators:</p> <list type="bulleted"> <item><c>B: binary_alloc</c></item> + <item><c>C: sbmbc_alloc</c></item> <item><c>D: std_alloc</c></item> <item><c>E: ets_alloc</c></item> <item><c>F: fix_alloc</c></item> @@ -300,11 +326,11 @@ 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> @@ -395,6 +421,20 @@ threshold will be placed in singleblock carriers. Blocks smaller than this threshold will be placed in multiblock carriers.</item> + <tag><marker id="M_sbmbcs"><c><![CDATA[+M<S>sbmbcs <size>]]></c></marker></tag> + <item> + Small block multiblock carrier size (in bytes). Memory blocks smaller + than the small block multiblock carrier threshold + (<seealso marker="#M_sbmbct">sbmbct</seealso>) will be placed in + multiblock carriers used for small blocks only. This parameter + determines the size of such carriers. + </item> + <tag><marker id="M_sbmbct"><c><![CDATA[+M<S>sbmbct <size>]]></c></marker></tag> + <item> + Small block multiblock carrier threshold (in bytes). Memory blocks + smaller than this threshold will be placed in multiblock carriers + used for small blocks only. + </item> <tag><marker id="M_smbcs"><c><![CDATA[+M<S>smbcs <size>]]></c></marker></tag> <item> Smallest (<c>mseg_alloc</c>) multiblock carrier size (in @@ -403,10 +443,10 @@ 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> <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): + <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 (<c>N</c> equals the number of scheduler threads):</p> <taglist> <tag><c>temp_alloc</c></tag> <item><c>N + 1</c> instances.</item> @@ -417,10 +457,10 @@ <c>16</c>. <c>16</c> instances when <c>N</c> is greater than <c>16</c>.</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>. + <p><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>.</p> </item> </taglist> <p>Currently the following flags are available for configuration of |