Re: [doc fix] Correct calculation of vm.nr_hugepages

On 2018-02-20 02:43:32 +0000, Tsunakawa, Takayuki wrote:
> diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
> index d162acb..1aed070 100644
> --- a/doc/src/sgml/runtime.sgml
> +++ b/doc/src/sgml/runtime.sgml
> @@ -1472,14 +1472,14 @@ export PG_OOM_ADJUST_VALUE=0
> the kernel setting <varname>vm.nr_hugepages</varname>. To estimate the
> number of huge pages needed, start <productname>PostgreSQL</productname>
> without huge pages enabled and check the
> - postmaster's <varname>VmPeak</varname> value, as well as the system's
> + postmaster's anonymous shared memory segment size, as well as the system's
> huge page size, using the <filename>/proc</filename> file system. This might
> look like:
> <programlisting>
> $ <userinput>head -1 $PGDATA/postmaster.pid</userinput>
> 4170
> -$ <userinput>grep ^VmPeak /proc/4170/status</userinput>
> -VmPeak: 6490428 kB
> +$ <userinput>pmap 4170 | awk '/rw-s/ && /zero/ {print $2}'</userinput>
> +6490428K
> $ <userinput>grep ^Hugepagesize /proc/meminfo</userinput>
> Hugepagesize: 2048 kB
> </programlisting>

One disadvantage of this is that it relies on the presence of pmap,
which IIRC is not installed by default in a number of distributions. Are
we concerned about that?

Greetings,

Andres Freund