Message-ID: <54CA7DCC.5050209@gmail.com>
Date: Thu, 29 Jan 2015 13:37:00 -0500
From: John Scalia <jayknowsunix@gmail.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
Subject: Re: hugepage configuration for V.9.4.0
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On 1/29/2015 1:18 PM, Tom Lane wrote:
> John Scalia <jayknowsunix@gmail.com> writes:
>> I'm certain that I'm no expert for this one, as I've never had to configure this parameter for anything prior, but I continue to get a startup error when I try to use this. The
>> server is a VM running CentOS 6.5 with 4 Gb allocated to it. When I started setting "huge_pages = on", the server reported:
>> %FATAL: could not map anonymous shared memory: Cannot allocate memory
>> %HINT: this error usually means that PostgreSQL's request for a shared memory segment exceeded available memory, swap space, or huge pages. To reduce the request size (currently
>> 1124876288 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.
>> Further research showed that server's /sys/kernel/mm/transparent_hugepage/enabled file contained "[always] madvise never"
>> As I was concerned about the "always" setting, I used "cat madvise > " to the file so it reported "always [madvise] never" I even set this in /etc/rc.local and performed a reboot.
> FWIW, I think that the transparent_hugepage setting is irrelevant to this.
> The whole point here is that we're explicitly asking for a hugepage memory
> segment, so the OS doesn't have to try to make it transparent.
>
> What might be happening is that when requesting a hugepage segment, we
> actually round up the request (here claimed to be 1124876288 bytes)
> to the next 2MB boundary.  Is it possible your kernel settings are
> such that the slightly larger request fails?
>
> Also, there may well be request limits that apply specifically to hugepage
> segments; I don't know too much about that.
>
> 			regards, tom lane
>
Thanks to all that responded. I really kind of figured that a 4Gb server was too small, but I'm limited to that by our virtual server configuration system. I'll look into how this 
kernel is configured, Tom, but is there something specific that you know of for me to examine? FWIW, I didn't build this kernel as I have to choose one from the server build page 
when I try to create the system. I guess I could download the sources to do a build on it, once it's running, but I'm think it's really not the worth the effort for one this small.


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