On Thu 26-07-18 18:18:53, Mike Rapoport wrote: > On Thu, Jul 26, 2018 at 04:20:39PM +0200, Michal Hocko wrote: > > On Thu 26-07-18 06:01:06, Matthew Wilcox wrote: > > > On Thu, Jul 26, 2018 at 03:22:02PM +0300, Mike Rapoport wrote: > > > > +Memory Allocation Controls > > > > +========================== > > > > > > Perhaps call this section "Memory Allocation Flags" instead? > > > > > > > +Linux provides a variety of APIs for memory allocation from direct > > > > +calls to page allocator through slab caches and vmalloc to allocators > > > > +of compressed memory. Although these allocators have different > > > > +semantics and are used in different circumstances, they all share the > > > > +GFP (get free page) flags that control behavior of each allocation > > > > +request. > > > > > > While this isn't /wrong/, I think it might not be the most useful way > > > of explaining what the GFP flags are to someone who's just come across > > > them in some remote part of the kernel. How about this paragraph instead? > > > > > > Functions which need to allocate memory often use GFP flags to express > > > how that memory should be allocated. The GFP acronym stands for "get > > > free pages", the underlying memory allocation function. > > > > OK. > > > > > Not every GFP > > > flag is allowed to every function which may allocate memory. Most > > > users will want to use a plain ``GFP_KERNEL`` or ``GFP_ATOMIC``. > > > > Or rather than mentioning the two just use "Useful GFP flag > > combinations" comment segment from gfp.h > > The comment there includes GFP_DMA, GFP_NOIO etc so I'd prefer Matthew's > version and maybe even omit GFP_ATOMIC from it. > > Some grepping shows that roughly 80% of allocations are GFP_KERNEL, 12% are > GFP_ATOMIC and ... I didn't count the usage of other flags ;-) Well, I will certainly not insist... I don't know who is the expected audience of this documentation. That section was meant for kernel developers to know which of the high level flags to use. -- Michal Hocko SUSE Labs
