Kernel Parameter "mem" - meminfo Disparity

[Matt Roth]

Jeff,

Thanks for your response.  To answer your question...

>> I have a Dell PowerEdge 6850 running Fedora Core 3 with 12 GBytes of 
>> RAM.  Due to limitations of a PCI card I'm installing, I wish to limit 
>> the system memory to just under 4 GBytes using the kernel parameter 
>> "mem".  When I do this, the machine boots fine and the PCI card operates 
>> properly, but "/proc/meminfo" and "free" report 2.6 GBytes of available 
>> memory. 
>
>What pci card would cause you to need to limit the  kernel access to
>memory?

The card is a Level 5 Networks EF1-21022T NIC.  Here is a quote from the product bulletin that ships with the card.

------------------------------------------------------------

Errata 1 - Support for machines with 4 gigabytes or more of memory.

Problem Summary

The EtherFabric software requires that the target machines provide a fully consistent DMA between the PCI device and the mapped host memory buffers.  The EF1-21022T NIC supports 32-bit PCI addressing which allows access to only the lower 4 Gigabytes of PCI address space.

Target machines supporting IOMMU provide a method for 32-bit PCI devices to directly access physical memory that is above the 4 Gigabyte limit.

------------------------------------------------------------

Unfortunately, our machine does not fall into this category.  Please note that the free technical support from Level 5 Networks has been outstanding and that they are due to release a new card supporting 64-bit PCI addressing in the near future.  They have offered us to trade-in our card for the new one at no additional charge.  With the memory limitation and on our machine with 1 GByte of RAM their card works well, and they created custom drivers and software for our kernel in approximately three business days.

If you are considering buying a new NIC, be aware of this limitation but don't exclude Level 5 from your options if it doesn't apply to you.

Matthew Roth
InterMedia Marketing Solutions
Software Engineer and Systems Developer