Here is a map of physical memory before any user processes are executed. The column on the left gives the starting address of the item, numbers in italics are approximate. The column in the middle names the item(s). The column on the far right gives the relevant routine or variable name or explains the entry.
device-inits that acquire memory are(main.c): profil_buffer, con_init, psaux_init, rd_init, scsi_dev_init.
Note that all memory not marked as FREE is RESERVED (mem_init).
RESERVED pages belong to the kernel and are never freed or swapped.