Enrico Fraccaroli (Galfurian)
153 lines
6.0 KiB
C
153 lines
6.0 KiB
C
/// @file gfp.h
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/// @brief List of Get Free Pages (GFP) Flags.
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/// @copyright (c) 2014-2022 This file is distributed under the MIT License.
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/// See LICENSE.md for details.
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#pragma once
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/// Type used for GFP_FLAGS.
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typedef unsigned int gfp_t;
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/// @defgroup GFP The Get Free Pages (GFP) flags
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/// @brief Sets of GFP defines.
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/// @{
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/// @defgroup gfp_bitmasks Bitmasks
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/// @brief Plain integer GFP bitmasks. Do not use this directly.
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/// @{
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#define ___GFP_DMA 0x001U ///< DMA
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#define ___GFP_HIGHMEM 0x002U ///< HIGHMEM
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#define ___GFP_DMA32 0x004U ///< DMA32
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#define ___GFP_RECLAIMABLE 0x010U ///< RECLAIMABLE
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#define ___GFP_HIGH 0x020U ///< HIGH
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#define ___GFP_IO 0x040U ///< IO
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#define ___GFP_FS 0x080U ///< FS
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#define ___GFP_ZERO 0x100U ///< ZERO
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#define ___GFP_ATOMIC 0x200U ///< ATOMIC
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#define ___GFP_DIRECT_RECLAIM 0x400U ///< DIRECT_RECLAIM
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#define ___GFP_KSWAPD_RECLAIM 0x800U ///< KSWAPD_RECLAIM
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/// @}
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/// @defgroup zone_modifiers Zone Modifiers
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/// @brief Physical address zone modifiers (see linux/mmzone.h - low four bits)
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/// @details
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/// Do not put any conditional on these. If necessary modify the definitions
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/// without the underscores and use them consistently. The definitions here may
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/// be used in bit comparisons.
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/// @{
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#define __GFP_DMA ___GFP_DMA ///< DMA
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#define __GFP_HIGHMEM ___GFP_HIGHMEM ///< HIGHMEM
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#define __GFP_DMA32 ___GFP_DMA32 ///< DMA32
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/// All of the above.
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#define GFP_ZONEMASK (__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32)
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/// @}
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/// @defgroup WatermarkModifiers Watermark Modifiers
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/// @brief Controls access to emergency reserves.
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/// @{
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/// @brief Indicates that the caller cannot reclaim or sleep and is
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/// high priority. Users are typically interrupt handlers. This may be
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/// used in conjunction with %__GFP_HIGH.
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#define __GFP_ATOMIC ___GFP_ATOMIC
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/// @brief Indicates that the caller is high-priority and that granting
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/// the request is necessary before the system can make forward progress.
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/// For example, creating an IO context to clean pages.
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#define __GFP_HIGH ___GFP_HIGH
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/// @}
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/// @defgroup ReclaimModifiers Reclaim Modifiers
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/// @brief Enable reclaim operations on a specific region of memory.
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/// @{
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/// @brief Can start physical IO.
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#define __GFP_IO ___GFP_IO
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/// @brief Can call down to the low-level FS. Clearing the flag avoids the
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/// allocator recursing into the filesystem which might already be holding
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/// locks.
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#define __GFP_FS ___GFP_FS
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/// @brief Indicates that the caller may enter direct reclaim.
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/// This flag can be cleared to avoid unnecessary delays when a fallback
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/// option is available.
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#define __GFP_DIRECT_RECLAIM ___GFP_DIRECT_RECLAIM
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/// @brief Indicates that the caller wants to wake kswapd when
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/// the low watermark is reached and have it reclaim pages until the high
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/// watermark is reached. A caller may wish to clear this flag when fallback
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/// options are available and the reclaim is likely to disrupt the system. The
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/// canonical example is THP allocation where a fallback is cheap but
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/// reclaim/compaction may cause indirect stalls.
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#define __GFP_KSWAPD_RECLAIM ___GFP_KSWAPD_RECLAIM
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/// @brief Is shorthand to allow/forbid both direct and kswapd reclaim.
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#define __GFP_RECLAIM (___GFP_DIRECT_RECLAIM | ___GFP_KSWAPD_RECLAIM)
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/// @}
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/// @defgroup gfp_flag_combinations Flag Combinations
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/// @brief Useful GFP flag combinations.
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/// @details
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/// Useful GFP flag combinations that are commonly used. It is recommended
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/// that subsystems start with one of these combinations and then set/clear
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/// the flags as necessary.
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/// @{
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/// @brief Users can not sleep and need the allocation to succeed. A lower
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/// watermark is applied to allow access to "atomic reserves"
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#define GFP_ATOMIC (__GFP_HIGH | __GFP_ATOMIC | __GFP_KSWAPD_RECLAIM)
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/// @brief is typical for kernel-internal allocations. The caller requires
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/// %ZONE_NORMAL or a lower zone for direct access but can direct reclaim.
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#define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
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/// @brief is for kernel allocations that should not stall for direct
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/// reclaim, start physical IO or use any filesystem callback.
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#define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM)
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/// @brief will use direct reclaim to discard clean pages or slab pages
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/// that do not require the starting of any physical IO.
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/// Please try to avoid using this flag directly and instead use
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/// memalloc_noio_{save,restore} to mark the whole scope which cannot
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/// perform any IO with a short explanation why. All allocation requests
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/// will inherit GFP_NOIO implicitly.
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#define GFP_NOIO (__GFP_RECLAIM)
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/// @brief will use direct reclaim but will not use any filesystem interfaces.
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/// Please try to avoid using this flag directly and instead use
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/// memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't
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/// recurse into the FS layer with a short explanation why. All allocation
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/// requests will inherit GFP_NOFS implicitly.
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#define GFP_NOFS (__GFP_RECLAIM | __GFP_IO)
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/// @brief is for userspace allocations that also need to be directly
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/// accessibly by the kernel or hardware. It is typically used by hardware
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/// for buffers that are mapped to userspace (e.g. graphics) that hardware
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/// still must DMA to. cpuset limits are enforced for these allocations.
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#define GFP_USER (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
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/// @brief exists for historical reasons and should be avoided where possible.
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/// The flags indicates that the caller requires that the lowest zone be
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/// used (%ZONE_DMA or 16M on x86-64). Ideally, this would be removed but
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/// it would require careful auditing as some users really require it and
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/// others use the flag to avoid lowmem reserves in %ZONE_DMA and treat the
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/// lowest zone as a type of emergency reserve.
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#define GFP_DMA (__GFP_DMA)
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/// @brief is for userspace allocations that may be mapped to userspace,
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/// do not need to be directly accessible by the kernel but that cannot
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/// move once in use. An example may be a hardware allocation that maps
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/// data directly into userspace but has no addressing limitations.
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#define GFP_HIGHUSER (GFP_USER | __GFP_HIGHMEM)
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/// @}
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/// @}
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