Mastering Linux Kernel Development

Zone descriptor structure

The mmzone.h header also declares struct zone, which serves as zone descriptor. Following is a code snippet of structure definition and is well commented. We shall follow on with descriptions of a few important fields:

struct zone { /* Read-mostly fields */ /* zone watermarks, access with *_wmark_pages(zone) macros */ unsigned long watermark[NR_WMARK]; unsigned long nr_reserved_highatomic; /* * 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 being tons of freeable ram on the higher zones). ...