参照元†
/*
* 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.
*/
#define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
#define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
#define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM)
#define GFP_NOIO (__GFP_RECLAIM)
#define GFP_NOFS (__GFP_RECLAIM | __GFP_IO)
#define GFP_TEMPORARY (__GFP_RECLAIM | __GFP_IO | __GFP_FS | \
__GFP_RECLAIMABLE)
#define GFP_USER (__GFP_RECLAIM | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
#define GFP_DMA __GFP_DMA
#define GFP_DMA32 __GFP_DMA32
#define GFP_HIGHUSER (GFP_USER | __GFP_HIGHMEM)
#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE)
#define GFP_TRANSHUGE ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN) & \
~__GFP_KSWAPD_RECLAIM)
コメント†