IMHO the memory is getting fragmented a lot.
Here's the fragmentation info. There's hardly any segment above 64KB available after 2 days of runtime.

Normal: 1024*4kB 1636*8kB 394*16kB 12*32kB 1*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 23936kB

Here's how I got this info

echo m > /proc/sysrq-trigger
dmesg