[$] GFP flags and the end of __GFP_ATOMIC

Memory allocation within the kernel is a complex business. The amount ofphysical memory available on any given system will be strictly limited,meaning that an allocation request can often only be satisfied by takingmemory from somebody else, but some of the options for reclaiming memorymay not be available when a request is made. Additionally,some allocation requests haverequirements dictating where that memory can be placed or how quickly theallocation must be made. The kernel'smemory-allocation functions have long supported a set of "GFP flags" usedto describe the requirements of each specific request. Those flags willprobably undergo some changes soon as the result of thispatch set posted by Mel Gorman; that provides an opportunity to look atthose flags in some detail.