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Document the B and L MALLOC_OPTIONS.

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Jason Evans 2007-11-27 03:18:26 +00:00
parent 5ea8413d0a
commit 77cfb3fec2
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=173969
1 changed files with 26 additions and 1 deletions
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27
lib/libc/stdlib/malloc.3
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@ -32,7 +32,7 @@
.\" @(#)malloc.3 8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd June 15, 2007
.Dd October 1, 2007
.Dt MALLOC 3
.Os
.Sh NAME
@ -177,6 +177,19 @@ flags being set) become fatal.
The process will call
.Xr abort 3
in these cases.
.It B
Increase/decrease the per-arena lock contention threshold at which a thread is
randomly re-assigned to an arena.
This dynamic load balancing tends to push threads away from highly contended
arenas, which avoids worst case contention scenarios in which threads
disproportionately utilize arenas.
However, due to the highly dynamic load that applications may place on the
allocator, it is impossible for the allocator to know in advance how sensitive
it should be to contention over arenas.
Therefore, some applications may benefit from increasing or decreasing this
threshold parameter.
This option is not available for some configurations (non-PIC).
This option can be specified multiple times.
.It H
Use
.Xr madvise 2
@ -204,6 +217,18 @@ This is intended for debugging and will impact performance negatively.
Increase/decrease the virtual memory chunk size by a factor of two.
The default chunk size is 1 MB.
This option can be specified multiple times.
.It L
Increase/decrease the per-arena number of slots for lazy deallocation.
Lazy deallocation can decrease lock contention, especially for programs that use
the producer/consumer model.
The default is 256 slots per arena (so
.Ev MALLOC_OPTIONS=lllllllll
will disable lazy deallocation), but note that due to algorithmic details, the
cache is typically flushed well before it completely fills.
This option has no impact unless there are multiple CPUs, and lazy deallocation
does not activate unless the program uses multiple threads.
This option is not available for some configurations (non-PIC).
This option can be specified multiple times.
.It N
Increase/decrease the number of arenas by a factor of two.
The default number of arenas is four times the number of CPUs, or one if there