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Compiling the Linux Kernel for More than 1GB of RAM

/ October 3, 2016 — GNU/Linux

Agatha recently purchased another stick of 512MB RAM. It turns out that by default you need to change the kernel for it to use more than 1GB of RAM. Actually, the cutoff is technically at 960MB. Here is the memory info with 1.5GB of RAM installed, but with high memory support disabled:

 
usr-1@srv-1 proc $ cat /proc/meminfo
total:    used:    free:  shared: buffers:  cached:
Mem:  926294016 249950208 676343808        0 12587008 137678848
Swap:        0        0        0
MemTotal:       904584 kB
MemFree:        660492 kB
MemShared:           0 kB
Buffers:         12292 kB
Cached:         134452 kB
SwapCached:          0 kB
Active:          96724 kB
Inactive:       118636 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       904584 kB
LowFree:        660492 kB
SwapTotal:           0 kB
SwapFree:            0 kB
usr-1@srv-1 proc $

The options you need to set in the 2.4 kernel are:

CONFIG_HIGHMEM4G=y
CONFIG_HIGHMEM=y

After a reboot, the memory now looks like this:

usr-1@srv-1 usr-1 $ cat /proc/meminfo
total:    used:    free:  shared: buffers:  cached:
Mem:  1588539392 267857920 1320681472        0 14606336 181346304
Swap:        0        0        0
MemTotal:      1551308 kB
MemFree:       1289728 kB
MemShared:           0 kB
Buffers:         14264 kB
Cached:         177096 kB
SwapCached:          0 kB
Active:          84220 kB
Inactive:       144420 kB
HighTotal:      655344 kB
HighFree:       436384 kB
LowTotal:       895964 kB
LowFree:        853344 kB
SwapTotal:           0 kB
SwapFree:            0 kB
usr-1@srv-1 usr-1 $

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