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Re: [PATCH 2/2] Document the M_ARENA_* mallopt parameters
On 10/10/2016 01:26 PM, Siddhesh Poyarekar wrote:
> The M_ARENA_* mallopt parameters are in wide use in production to
> control the number of arenas that a long lived process creates and
> hence there is no point in stating that this interface is non-public.
> Document this interface and remove the obsolete comment.
>
> * manual/memory.texi (M_ARENA_TEST): Add documentation.
> (M_ARENA_MAX): Likewise.
> * malloc/malloc.c: Remove obsolete comment.
> ---
> malloc/malloc.c | 1 -
> manual/memory.texi | 21 +++++++++++++++++++++
> 2 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 09e004b..0011a6d 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -1718,7 +1718,6 @@ static struct malloc_par mp_ =
> };
>
>
> -/* Non public mallopt parameters. */
> #define M_ARENA_TEST -7
> #define M_ARENA_MAX -8
>
> diff --git a/manual/memory.texi b/manual/memory.texi
> index 222f126..b98dcf2 100644
> --- a/manual/memory.texi
> +++ b/manual/memory.texi
> @@ -1153,6 +1153,27 @@ order to return memory to the system.
>
> This parameter can also be set for the process at startup by setting the
> environment variable @code{MALLOC_TRIM_THRESHOLD_} to the desired value.
> +
> +@item M_ARENA_TEST
This description of an arena doesn't belong here, it belongs higher up in the
manual, and in fact I would suggest the following:
- Move 3.2.2.6 "Efficiency considerations for malloc" up to just under
"Dynamic Memory allocation" and put it under a new subsection "The GNU allocator".
- Under "The GNU allocator" give a brief 1 paragraph description of how
the allocator works e.g. https://sourceware.org/glibc/wiki/MallocInternals
and talk about arenas.
> +An arena is a memory pool that is allocated to act as a heap alongside the
> +system heap that the kernel creates for the process. This is to provide
> +multiple heap structures for multiple threads of a process to reduce contention
> +between them. The limit to the number of such arenas per process is determined
> +by the number of cores of the system and whether it is a 32-bit or a 64-bit
> +processor.
You don't say what M_ARENA_TEST is for?
> +
> +The value is ignored if @code{M_ARENA_MAX} is set either via @code{mallopt} or
> +via the @code{MALLOC_ARENA_MAX} environment variable.
> +
> +This parameter can also be set for the process at startup by setting the
> +environment variable @code{MALLOC_ARENA_TEST} to the desired value.
What is the default?
> +
> +@item M_ARENA_MAX
> +This parameter sets the number of arenas to use regardless of the number of
> +cores in the system.
> +
> +This parameter can also be set for the process at startup by setting the
> +environment variable @code{MALLOC_ARENA_MAX} to the desired value.
What is the default?
> @end table
>
> @end deftypefun
>
--
Cheers,
Carlos.