diff options
Diffstat (limited to 'erts/doc')
| -rw-r--r-- | erts/doc/src/erts_alloc.xml | 86 |
1 files changed, 47 insertions, 39 deletions
diff --git a/erts/doc/src/erts_alloc.xml b/erts/doc/src/erts_alloc.xml index c73cdfd290..2ffb55c6ab 100644 --- a/erts/doc/src/erts_alloc.xml +++ b/erts/doc/src/erts_alloc.xml @@ -75,10 +75,6 @@ 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> is always enabled and cannot be disabled. <c>mseg_alloc</c> is always enabled if it is @@ -86,9 +82,7 @@ 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. <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> + 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 @@ -106,20 +100,15 @@ 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>), 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 + 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. 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 + carriers. 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> @@ -140,9 +129,7 @@ <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. The size of multiblock carriers - for small blocks is determined by the small block multiblock - carrier size (<seealso marker="#M_sbmbcs">sbmbcs</seealso>). + <c>lmbcs</c> parameter, though. 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 @@ -183,6 +170,15 @@ used. The time complexity is proportional to log N, where N is the number of free blocks.</p> </item> + <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> + <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> + </item> <tag>Good fit</tag> <item> <p>Strategy: Try to find the best fit, but settle for the best fit @@ -219,11 +215,6 @@ but can only satisfy a limited amount of requests.</p> </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> @@ -245,7 +236,6 @@ 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> @@ -319,10 +309,42 @@ subsystem identifier, only the specific allocator identified will be effected:</p> <taglist> - <tag><marker id="M_as"><c><![CDATA[+M<S>as bf|aobf|aoff|gf|af]]></c></marker></tag> + <tag><marker id="M_acul"><c><![CDATA[+M<S>acul <utilization>|de]]></c></marker></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. Currently the default + is zero. 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. 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 <c>aoff</c> and the <c>aoffcaobf</c> strategies 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>aoffcaobf</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|aoffcaobf|gf|af]]></c></marker></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>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></marker></tag> @@ -416,20 +438,6 @@ 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_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 |