+ * Useful GFP flag combinations that are commonly used. It is recommended
+ * that subsystems start with one of these combinations and then set/clear
+ * __GFP_FOO flags as necessary.
+ *
+ * GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower
+ * watermark is applied to allow access to "atomic reserves"
+ *
+ * GFP_KERNEL is typical for kernel-internal allocations. The caller requires
+ * ZONE_NORMAL or a lower zone for direct access but can direct reclaim.
+ *
+ * GFP_NOWAIT is for kernel allocations that should not stall for direct
+ * reclaim, start physical IO or use any filesystem callback.
+ *
+ * GFP_NOIO will use direct reclaim to discard clean pages or slab pages
+ * that do not require the starting of any physical IO.
+ *
+ * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces.
+ *
+ * GFP_USER is for userspace allocations that also need to be directly
+ * accessibly by the kernel or hardware. It is typically used by hardware
+ * for buffers that are mapped to userspace (e.g. graphics) that hardware
+ * still must DMA to. cpuset limits are enforced for these allocations.
+ *
+ * GFP_DMA exists for historical reasons and should be avoided where possible.
+ * The flags indicates that the caller requires that the lowest zone be
+ * used (ZONE_DMA or 16M on x86-64). Ideally, this would be removed but
+ * it would require careful auditing as some users really require it and
+ * others use the flag to avoid lowmem reserves in ZONE_DMA and treat the
+ * lowest zone as a type of emergency reserve.
+ *
+ * GFP_DMA32 is similar to GFP_DMA except that the caller requires a 32-bit
+ * address.
+ *
+ * GFP_HIGHUSER is for userspace allocations that may be mapped to userspace,
+ * do not need to be directly accessible by the kernel but that cannot
+ * move once in use. An example may be a hardware allocation that maps
+ * data directly into userspace but has no addressing limitations.
+ *
+ * GFP_HIGHUSER_MOVABLE is for userspace allocations that the kernel does not
+ * need direct access to but can use kmap() when access is required. They
+ * are expected to be movable via page reclaim or page migration. Typically,
+ * pages on the LRU would also be allocated with GFP_HIGHUSER_MOVABLE.
+ *
+ * GFP_TRANSHUGE is used for THP allocations. They are compound allocations
+ * that will fail quickly if memory is not available and will not wake
+ * kswapd on failure.