Linux Kernel

Linux VM Notes #2 Zones Each zone is described by a struct zone_struct. zone_structs keep track of information like page usage statistics, free area information and locks. Here is the zone struct.. /* * On machines where it is needed (eg PCs) we divide physical memory * into multiple physical zones. On a PC we have 3 zones: * * ZONE_DMA < 16 MB ISA DMA capable memory * ZONE_NORMAL 16-896 MB direct mapped by the kernel * ZONE_HIGHMEM > 896 MB only page cache and user processes */ struct zone { /* Fields commonly accessed by the page allocator */ unsigned long free_pages; unsigned long pages_min, pages_low, pages_high; /* * We don't know if the memory that we're going to allocate will be freeable * or/and it will be released eventually, so to avoid totally wasting several * GB of ram we must reserve some of the lower zone memory (otherwise we risk * to run OOM on the lower zones despite there's tons of freeable ram * on the higher zones). Th