GFP_LEVEL_MASK is used to allow the pass through of page allocator
flags. Currently these are
#define GFP_LEVEL_MASK (__GFP_WAIT|__GFP_HIGH|__GFP_IO|__GFP_FS| \
__GFP_COLD|__GFP_NOWARN|__GFP_REPEAT| \
__GFP_NOFAIL|__GFP_NORETRY|__GFP_COMP| \
__GFP_NOMEMALLOC|__GFP_HARDWALL|__GFP_THISNODE|
__GFP_MOVABLE)
Some of these flags control page allocator reclaim and fallback
behavior. If they are specified for a slab alloc operation then they
are effective if a new slab has to be allocated. These are
1. Reclaim control
__GFP_WAIT
__GFP_IO
__GFP_FS
__GFP_NOWARN
__GFP_REPEAT
__GFP_NOFAIL
__GFP_NORETRY
2. Reserve control
__GFP_HIGH
__GFP_NOMEMALLOC
2. Fallback control
__GFP_HARDWALL (cpuset contraints)
__GFP_THISNODE (handled by SLAB on its own, SLUB/SLOB pass through)
AFAIK these make sense.
Then there are some other flags. I am wondering why they are in
GFP_LEVEL_MASK?
__GFP_COLD Does not make sense for slab allocators since we have
to touch the page immediately.
__GFP_COMP No effect. Added by the page allocator on their own
if a higher order allocs are used for a slab.
__GFP_MOVABLE The movability of a slab is determined by the
options specified at kmem_cache_create time. If this is
specified at kmalloc time then we will have some random
slabs movable and others not.
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