Hi, I was wondering if anyone would know the cons of running a PAE kernel...? I have a 4GB pc and was wondering if it was worth going the PAE way to gain those exta 700MB... In the past, I heard that these 700MB were normally reserved for bios or chipset stuff... And that running in PAE would slow down some processes. By the way, I know 64 bits would solve this dilemn but right now I am 32bits... Thx, JD
On Thursday 22 July 2010, John Doe wrote:> Hi, > > I was wondering if anyone would know the cons of running a PAE kernel...? > I have a 4GB pc and was wondering if it was worth going the PAE way to gain > those exta 700MB... > In the past, I heard that these 700MB were normally reserved for bios or > chipset stuff... > And that running in PAE would slow down some processes. > By the way, I know 64 bits would solve this dilemn but right now I am > 32bits...There is no general answer. Getting more memory could for some workloads be critical. On the other hand, other loads might not care much about the extra few hundred megs but instead suffer some PAE related slowdown. Good news though, trivial to test. Just reboot with the PAE kernel, check the performance of your workload. If you see improvment stay on PAE, else go back. /Peter -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 189 bytes Desc: This is a digitally signed message part. URL: <http://lists.centos.org/pipermail/centos/attachments/20100722/b20a66be/attachment.sig>
On 7/22/2010 3:25 AM, John Doe wrote:> > I have a 4GB pc and was wondering if it was worth going the PAE way to gain > those exta 700MB...Very few programs can use PAE to get at that extra RAM. Can the programs you run do this? Is your CPU 64-bit capable? That's generally a better idea than PAE. Keep in mind that PAE is Pentium Pro era technology.
JD, On 22/07/10 10:25, John Doe wrote:> I was wondering if anyone would know the cons of running a PAE kernel...? > I have a 4GB pc and was wondering if it was worth going the PAE way to gain > those exta 700MB...You should use 64 bit if possible but if you're seeing 3.2GB, it's more likely that your motherboard is not capable (I have one of those here right now).> In the past, I heard that these 700MB were normally reserved for bios or chipset > stuff...It still is, even with with 64 bit. If your motherboard supports remapping this memory with 64 bit you can use the whole 4GB. Otherwise you're limited to 3.2: hakan at photon:~$ free -m total used free shared buffers cached Mem: 3262 1972 1290 0 103 737 -/+ buffers/cache: 1131 2131 Swap: 7812 308 7504 hakan at photon:~$ arch x86_64
On 22/07/2010 11:25, John Doe wrote:> Hi, > > I have a 4GB pc and was wondering if it was worth going the PAE way to gain > those exta 700MB... > In the past, I heard that these 700MB were normally reserved for bios or chipset > stuff...I installed a 32 bit centos and with the non-pae kernel it shows 3.3 gb for me too. I had a look at bios but there is nothing of interest, nothing obvious at least. Asking myself if it is "normally" as you said. -- Regards, Markus
Hi John, On 22/07/10 19:56, JohnS wrote:> Try about 69Gbytes& What are you fiddling with? limits.conf?I think you read my mail too quickly and wrote a reply in similar speed. :) So did I read the original post too quickly and didn't realise he was complaining about the memory hole... You're right to say PAE goes to 64GB although in the past various distros had kernels compiled for different max addresses for various reasons. 4GB address space still applies to 32 bit apps. To use more than 4GB tricks as such (http://www.puschitz.com/TuningLinuxForOracle.shtml#ConfiguringVeryLargeMemory) need to be used. :) I haven't had to use these kinds of tricks for years since every machine I encounter has 64 bits and Oracle runs nicely on them perfectly happily. I miss reading through Puschitz's tips & tricks. Lately all Oracle versions run pretty much out of the box on CentOS/Upstream. No sense of satisfaction from seeing it running after battling with it for hours. :)