Kernel Parameter "mem" - meminfo Disparity

[Jeff Vian]

On Wed, 2005-09-07 at 11:03 -0400, Matt Roth wrote:
> List members,
> 
> 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?

> Can anyone explain this situation or help me resolve it?  If you need 
> anymore information than I have supplied, please request it.
> 
> System information:
> uname -a
> Linux immlx15.imm1 2.6.12-1.1376_FC3smp #1 SMP Fri Aug 26 23:51:16 EDT 
> 2005 x86_64 x86_64 x86_64 GNU/Linux
> 
> /proc/cmdline
> ro root=LABEL=/ quiet mem=4095M
> 

Maybe because you are slightly under the even 4G boundary it has to drop
lower to a logical boundary for memory access.  Just a guess since I
have never needed to use that trick on booting.

> /proc/meminfo
> MemTotal:      2809040 kB
> MemFree:       2693600 kB
> Buffers:         13308 kB
> Cached:          35052 kB
> SwapCached:          0 kB
> Active:          42056 kB
> Inactive:        29236 kB
> HighTotal:           0 kB
> HighFree:            0 kB
> LowTotal:      2809040 kB
> LowFree:       2693600 kB
> SwapTotal:     2096472 kB
> SwapFree:      2096472 kB
> Dirty:              60 kB
> Writeback:           0 kB
> Mapped:          28440 kB
> Slab:            19728 kB
> CommitLimit:   3500992 kB
> Committed_AS:    48392 kB
> PageTables:       1740 kB
> VmallocTotal: 34359738367 kB
> VmallocUsed:    275932 kB
> VmallocChunk: 34359461883 kB
> HugePages_Total:     0
> HugePages_Free:      0
> Hugepagesize:     2048 kB            
> 
> free -k
>              total       used       free     shared    buffers     cached
> Mem:       2809040     115136    2693904          0      13348      35012
> -/+ buffers/cache:      66776    2742264
> Swap:      2096472          0    2096472       
> 
> Thank you,
> 
> Matthew Roth
> InterMedia Marketing Solutions
> Software Engineer and Systems Developer
>