/* SPDX-License-Identifier: GPL-2.0 */ #ifndef __LINUX_GFP_TYPES_H #define __LINUX_GFP_TYPES_H #include <linux/bits.h> /* The typedef is in types.h but we want the documentation here */ #if 0 /** * typedef gfp_t - Memory allocation flags. * * GFP flags are commonly used throughout Linux to indicate how memory * should be allocated. The GFP acronym stands for get_free_pages(), * the underlying memory allocation function. Not every GFP flag is * supported by every function which may allocate memory. Most users * will want to use a plain ``GFP_KERNEL``. */ typedef unsigned int __bitwise gfp_t; #endif /* * In case of changes, please don't forget to update * include/trace/events/mmflags.h and tools/perf/builtin-kmem.c */ enum { … }; /* Plain integer GFP bitmasks. Do not use this directly. */ #define ___GFP_DMA … #define ___GFP_HIGHMEM … #define ___GFP_DMA32 … #define ___GFP_MOVABLE … #define ___GFP_RECLAIMABLE … #define ___GFP_HIGH … #define ___GFP_IO … #define ___GFP_FS … #define ___GFP_ZERO … /* 0x200u unused */ #define ___GFP_DIRECT_RECLAIM … #define ___GFP_KSWAPD_RECLAIM … #define ___GFP_WRITE … #define ___GFP_NOWARN … #define ___GFP_RETRY_MAYFAIL … #define ___GFP_NOFAIL … #define ___GFP_NORETRY … #define ___GFP_MEMALLOC … #define ___GFP_COMP … #define ___GFP_NOMEMALLOC … #define ___GFP_HARDWALL … #define ___GFP_THISNODE … #define ___GFP_ACCOUNT … #define ___GFP_ZEROTAGS … #ifdef CONFIG_KASAN_HW_TAGS #define ___GFP_SKIP_ZERO … #define ___GFP_SKIP_KASAN … #else #define ___GFP_SKIP_ZERO … #define ___GFP_SKIP_KASAN … #endif #ifdef CONFIG_LOCKDEP #define ___GFP_NOLOCKDEP … #else #define ___GFP_NOLOCKDEP … #endif #ifdef CONFIG_SLAB_OBJ_EXT #define ___GFP_NO_OBJ_EXT … #else #define ___GFP_NO_OBJ_EXT … #endif /* * Physical address zone modifiers (see linux/mmzone.h - low four bits) * * Do not put any conditional on these. If necessary modify the definitions * without the underscores and use them consistently. The definitions here may * be used in bit comparisons. */ #define __GFP_DMA … #define __GFP_HIGHMEM … #define __GFP_DMA32 … #define __GFP_MOVABLE … #define GFP_ZONEMASK … /** * DOC: Page mobility and placement hints * * Page mobility and placement hints * --------------------------------- * * These flags provide hints about how mobile the page is. Pages with similar * mobility are placed within the same pageblocks to minimise problems due * to external fragmentation. * * %__GFP_MOVABLE (also a zone modifier) indicates that the page can be * moved by page migration during memory compaction or can be reclaimed. * * %__GFP_RECLAIMABLE is used for slab allocations that specify * SLAB_RECLAIM_ACCOUNT and whose pages can be freed via shrinkers. * * %__GFP_WRITE indicates the caller intends to dirty the page. Where possible, * these pages will be spread between local zones to avoid all the dirty * pages being in one zone (fair zone allocation policy). * * %__GFP_HARDWALL enforces the cpuset memory allocation policy. * * %__GFP_THISNODE forces the allocation to be satisfied from the requested * node with no fallbacks or placement policy enforcements. * * %__GFP_ACCOUNT causes the allocation to be accounted to kmemcg. * * %__GFP_NO_OBJ_EXT causes slab allocation to have no object extension. */ #define __GFP_RECLAIMABLE … #define __GFP_WRITE … #define __GFP_HARDWALL … #define __GFP_THISNODE … #define __GFP_ACCOUNT … #define __GFP_NO_OBJ_EXT … /** * DOC: Watermark modifiers * * Watermark modifiers -- controls access to emergency reserves * ------------------------------------------------------------ * * %__GFP_HIGH indicates that the caller is high-priority and that granting * the request is necessary before the system can make forward progress. * For example creating an IO context to clean pages and requests * from atomic context. * * %__GFP_MEMALLOC allows access to all memory. This should only be used when * the caller guarantees the allocation will allow more memory to be freed * very shortly e.g. process exiting or swapping. Users either should * be the MM or co-ordinating closely with the VM (e.g. swap over NFS). * Users of this flag have to be extremely careful to not deplete the reserve * completely and implement a throttling mechanism which controls the * consumption of the reserve based on the amount of freed memory. * Usage of a pre-allocated pool (e.g. mempool) should be always considered * before using this flag. * * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. * This takes precedence over the %__GFP_MEMALLOC flag if both are set. */ #define __GFP_HIGH … #define __GFP_MEMALLOC … #define __GFP_NOMEMALLOC … /** * DOC: Reclaim modifiers * * Reclaim modifiers * ----------------- * Please note that all the following flags are only applicable to sleepable * allocations (e.g. %GFP_NOWAIT and %GFP_ATOMIC will ignore them). * * %__GFP_IO can start physical IO. * * %__GFP_FS can call down to the low-level FS. Clearing the flag avoids the * allocator recursing into the filesystem which might already be holding * locks. * * %__GFP_DIRECT_RECLAIM indicates that the caller may enter direct reclaim. * This flag can be cleared to avoid unnecessary delays when a fallback * option is available. * * %__GFP_KSWAPD_RECLAIM indicates that the caller wants to wake kswapd when * the low watermark is reached and have it reclaim pages until the high * watermark is reached. A caller may wish to clear this flag when fallback * options are available and the reclaim is likely to disrupt the system. The * canonical example is THP allocation where a fallback is cheap but * reclaim/compaction may cause indirect stalls. * * %__GFP_RECLAIM is shorthand to allow/forbid both direct and kswapd reclaim. * * The default allocator behavior depends on the request size. We have a concept * of so-called costly allocations (with order > %PAGE_ALLOC_COSTLY_ORDER). * !costly allocations are too essential to fail so they are implicitly * non-failing by default (with some exceptions like OOM victims might fail so * the caller still has to check for failures) while costly requests try to be * not disruptive and back off even without invoking the OOM killer. * The following three modifiers might be used to override some of these * implicit rules. Please note that all of them must be used along with * %__GFP_DIRECT_RECLAIM flag. * * %__GFP_NORETRY: The VM implementation will try only very lightweight * memory direct reclaim to get some memory under memory pressure (thus * it can sleep). It will avoid disruptive actions like OOM killer. The * caller must handle the failure which is quite likely to happen under * heavy memory pressure. The flag is suitable when failure can easily be * handled at small cost, such as reduced throughput. * * %__GFP_RETRY_MAYFAIL: The VM implementation will retry memory reclaim * procedures that have previously failed if there is some indication * that progress has been made elsewhere. It can wait for other * tasks to attempt high-level approaches to freeing memory such as * compaction (which removes fragmentation) and page-out. * There is still a definite limit to the number of retries, but it is * a larger limit than with %__GFP_NORETRY. * Allocations with this flag may fail, but only when there is * genuinely little unused memory. While these allocations do not * directly trigger the OOM killer, their failure indicates that * the system is likely to need to use the OOM killer soon. The * caller must handle failure, but can reasonably do so by failing * a higher-level request, or completing it only in a much less * efficient manner. * If the allocation does fail, and the caller is in a position to * free some non-essential memory, doing so could benefit the system * as a whole. * * %__GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller * cannot handle allocation failures. The allocation could block * indefinitely but will never return with failure. Testing for * failure is pointless. * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. * It should _never_ be used in non-sleepable contexts. * New users should be evaluated carefully (and the flag should be * used only when there is no reasonable failure policy) but it is * definitely preferable to use the flag rather than opencode endless * loop around allocator. * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is * not supported. Please consider using kvmalloc() instead. */ #define __GFP_IO … #define __GFP_FS … #define __GFP_DIRECT_RECLAIM … #define __GFP_KSWAPD_RECLAIM … #define __GFP_RECLAIM … #define __GFP_RETRY_MAYFAIL … #define __GFP_NOFAIL … #define __GFP_NORETRY … /** * DOC: Action modifiers * * Action modifiers * ---------------- * * %__GFP_NOWARN suppresses allocation failure reports. * * %__GFP_COMP address compound page metadata. * * %__GFP_ZERO returns a zeroed page on success. * * %__GFP_ZEROTAGS zeroes memory tags at allocation time if the memory itself * is being zeroed (either via __GFP_ZERO or via init_on_alloc, provided that * __GFP_SKIP_ZERO is not set). This flag is intended for optimization: setting * memory tags at the same time as zeroing memory has minimal additional * performance impact. * * %__GFP_SKIP_KASAN makes KASAN skip unpoisoning on page allocation. * Used for userspace and vmalloc pages; the latter are unpoisoned by * kasan_unpoison_vmalloc instead. For userspace pages, results in * poisoning being skipped as well, see should_skip_kasan_poison for * details. Only effective in HW_TAGS mode. */ #define __GFP_NOWARN … #define __GFP_COMP … #define __GFP_ZERO … #define __GFP_ZEROTAGS … #define __GFP_SKIP_ZERO … #define __GFP_SKIP_KASAN … /* Disable lockdep for GFP context tracking */ #define __GFP_NOLOCKDEP … /* Room for N __GFP_FOO bits */ #define __GFP_BITS_SHIFT … #define __GFP_BITS_MASK … /** * DOC: Useful GFP flag combinations * * Useful GFP flag combinations * ---------------------------- * * 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". * The current implementation doesn't support NMI and few other strict * non-preemptive contexts (e.g. raw_spin_lock). The same applies to %GFP_NOWAIT. * * %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_KERNEL_ACCOUNT is the same as GFP_KERNEL, except the allocation is * accounted to kmemcg. * * %GFP_NOWAIT is for kernel allocations that should not stall for direct * reclaim, start physical IO or use any filesystem callback. It is very * likely to fail to allocate memory, even for very small allocations. * * %GFP_NOIO will use direct reclaim to discard clean pages or slab pages * that do not require the starting of any physical IO. * Please try to avoid using this flag directly and instead use * memalloc_noio_{save,restore} to mark the whole scope which cannot * perform any IO with a short explanation why. All allocation requests * will inherit GFP_NOIO implicitly. * * %GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. * Please try to avoid using this flag directly and instead use * memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't * recurse into the FS layer with a short explanation why. All allocation * requests will inherit GFP_NOFS implicitly. * * %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. Note that kmalloc(..., GFP_DMA32) does not return DMA32 memory * because the DMA32 kmalloc cache array is not implemented. * (Reason: there is no such user in kernel). * * %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 and %GFP_TRANSHUGE_LIGHT are used for THP allocations. They * are compound allocations that will generally fail quickly if memory is not * available and will not wake kswapd/kcompactd on failure. The _LIGHT * version does not attempt reclaim/compaction at all and is by default used * in page fault path, while the non-light is used by khugepaged. */ #define GFP_ATOMIC … #define GFP_KERNEL … #define GFP_KERNEL_ACCOUNT … #define GFP_NOWAIT … #define GFP_NOIO … #define GFP_NOFS … #define GFP_USER … #define GFP_DMA … #define GFP_DMA32 … #define GFP_HIGHUSER … #define GFP_HIGHUSER_MOVABLE … #define GFP_TRANSHUGE_LIGHT … #define GFP_TRANSHUGE … #endif /* __LINUX_GFP_TYPES_H */
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