# 64-bit kernel shmmax - Suse

This is a discussion on 64-bit kernel shmmax - Suse ; Hi, What is the upper limit for shmmax on 64-bit kernel? -- GI...

1. ## 64-bit kernel shmmax

Hi,

What is the upper limit for shmmax on 64-bit kernel?

--
GI

2. ## Re: 64-bit kernel shmmax

On Sun, 12 Oct 2008, Ivan Gustin wrote:-

>Hi,
>
>What is the upper limit for shmmax on 64-bit kernel?

Well, for a 32bit kernel it's (only) 4GB. For a 64big kernel, it's a
little bit larger:

kernel.shmmax = 18446744073709551615

Which is one byte less than:

17,179,869,184 GiB (Gibibyte[0])
16,777,216 TiB (Tebibyte[0])
16,384 PiB (Pebibyte[0])
16 EiB (Exbibyte[0])

[0] Explanations of these can be found here:

Regards,
David Bolt

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3. ## Re: 64-bit kernel shmmax

David Bolt:
>> What is the upper limit for shmmax on 64-bit kernel?

> Well, for a 32bit kernel it's (only) 4GB. For a 64big kernel, it's a
> little bit larger:
> kernel.shmmax = 18446744073709551615

OK, tnx. That's 2^64, like 2^32 for 32-bit kernel. I was just wondering
if there is some other lower limit caused by kernel itself or by
something else.

--
GI

4. ## Re: 64-bit kernel shmmax

On 2008-10-12 23:08, David Bolt wrote:
> On Sun, 12 Oct 2008, Ivan Gustin wrote:-
>
>> Hi,
>>
>> What is the upper limit for shmmax on 64-bit kernel?

>
> Well, for a 32bit kernel it's (only) 4GB. For a 64big kernel, it's a
> little bit larger:
>
> kernel.shmmax = 18446744073709551615
>
> Which is one byte less than:
>
> 17,179,869,184 GiB (Gibibyte[0])
> 16,777,216 TiB (Tebibyte[0])
> 16,384 PiB (Pebibyte[0])
> 16 EiB (Exbibyte[0])
>
>
> [0] Explanations of these can be found here:
>
>
>
> Regards,
> David Bolt
>

Those numbers look like a recommended shmem tuning for Oracle :-)

/bb

5. ## Re: 64-bit kernel shmmax

On Mon, 13 Oct 2008 16:38:07 +0200
bb wrote:

>Those numbers look like a recommended shmem tuning for Oracle :-)
>

ROFLMAO!

(Recommended, but not yet optimum, right?) ;-)

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6. ## Re: 64-bit kernel shmmax

bb:
> Those numbers look like a recommended shmem tuning for Oracle :-)

:-D

Well, you're not far from truth. It's about growing PostgreSQL database.

--
GI