[PATCH 7/8] mm: split include/linux/gfp.h

Yury Norov
2022-07-01T12:58:00Z

gfp.h belongs to many include paths, and it causes circular dependencies
when, for example, trying to keep cpumask one-line wrappers in headers.

In many cases, sources need only gfp flags. This patch splits gfp.h by
moving flags to include/linux/gfp_flags.h. It helps to move trivial
wrappers from c-file to header in the following patch for cpumask.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
Documentation/core-api/mm-api.rst | 8 +-
MAINTAINERS | 1 +
include/linux/gfp.h | 334 +----------------------------
include/linux/gfp_flags.h | 338 ++++++++++++++++++++++++++++++
4 files changed, 344 insertions(+), 337 deletions(-)
create mode 100644 include/linux/gfp_flags.h

diff --git a/Documentation/core-api/mm-api.rst b/Documentation/core-api/mm-api.rst
index f5b2f92822c8..3886384b5047 100644
--- a/Documentation/core-api/mm-api.rst
+++ b/Documentation/core-api/mm-api.rst
@@ -22,16 +22,16 @@ Memory Allocation Controls
.. kernel-doc:: include/linux/gfp.h
:internal:

-.. kernel-doc:: include/linux/gfp.h
+.. kernel-doc:: include/linux/gfp_flags.h
:doc: Page mobility and placement hints

-.. kernel-doc:: include/linux/gfp.h
+.. kernel-doc:: include/linux/gfp_flags.h
:doc: Watermark modifiers

-.. kernel-doc:: include/linux/gfp.h
+.. kernel-doc:: include/linux/gfp_flags.h
:doc: Reclaim modifiers

-.. kernel-doc:: include/linux/gfp.h
+.. kernel-doc:: include/linux/gfp_flags.h
:doc: Useful GFP flag combinations

The Slab Cache
diff --git a/MAINTAINERS b/MAINTAINERS
index 3cf9842d9233..f808826509e5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12850,6 +12850,7 @@ T: quilt https://ozlabs.org/~akpm/mmotm/
T: quilt https://ozlabs.org/~akpm/mmots/
T: git git://github.com/hnaz/linux-mm.git
F: include/linux/gfp.h
+F: include/linux/gfp_flags.h
F: include/linux/memory_hotplug.h
F: include/linux/mm.h
F: include/linux/mmzone.h
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 2d2ccae933c2..15d60b385dfb 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -7,6 +7,7 @@
#include <linux/stddef.h>
#include <linux/linkage.h>
#include <linux/topology.h>
+#include <linux/gfp_flags.h>

/* The typedef is in types.h but we want the documentation here */
#if 0
@@ -24,339 +25,6 @@ typedef unsigned int __bitwise gfp_t;

struct vm_area_struct;

-/*
- * In case of changes, please don't forget to update
- * include/trace/events/mmflags.h and tools/perf/builtin-kmem.c
- */
-
-/* Plain integer GFP bitmasks. Do not use this directly. */
-#define ___GFP_DMA 0x01u
-#define ___GFP_HIGHMEM 0x02u
-#define ___GFP_DMA32 0x04u
-#define ___GFP_MOVABLE 0x08u
-#define ___GFP_RECLAIMABLE 0x10u
-#define ___GFP_HIGH 0x20u
-#define ___GFP_IO 0x40u
-#define ___GFP_FS 0x80u
-#define ___GFP_ZERO 0x100u
-#define ___GFP_ATOMIC 0x200u
-#define ___GFP_DIRECT_RECLAIM 0x400u
-#define ___GFP_KSWAPD_RECLAIM 0x800u
-#define ___GFP_WRITE 0x1000u
-#define ___GFP_NOWARN 0x2000u
-#define ___GFP_RETRY_MAYFAIL 0x4000u
-#define ___GFP_NOFAIL 0x8000u
-#define ___GFP_NORETRY 0x10000u
-#define ___GFP_MEMALLOC 0x20000u
-#define ___GFP_COMP 0x40000u
-#define ___GFP_NOMEMALLOC 0x80000u
-#define ___GFP_HARDWALL 0x100000u
-#define ___GFP_THISNODE 0x200000u
-#define ___GFP_ACCOUNT 0x400000u
-#define ___GFP_ZEROTAGS 0x800000u
-#ifdef CONFIG_KASAN_HW_TAGS
-#define ___GFP_SKIP_ZERO 0x1000000u
-#define ___GFP_SKIP_KASAN_UNPOISON 0x2000000u
-#define ___GFP_SKIP_KASAN_POISON 0x4000000u
-#else
-#define ___GFP_SKIP_ZERO 0
-#define ___GFP_SKIP_KASAN_UNPOISON 0
-#define ___GFP_SKIP_KASAN_POISON 0
-#endif
-#ifdef CONFIG_LOCKDEP
-#define ___GFP_NOLOCKDEP 0x8000000u
-#else
-#define ___GFP_NOLOCKDEP 0
-#endif
-/* If the above are modified, __GFP_BITS_SHIFT may need updating */
-
-/*
- * 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 ((__force gfp_t)___GFP_DMA)
-#define __GFP_HIGHMEM ((__force gfp_t)___GFP_HIGHMEM)
-#define __GFP_DMA32 ((__force gfp_t)___GFP_DMA32)
-#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
-#define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE)
-
-/**
- * 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.
- */
-#define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
-#define __GFP_WRITE ((__force gfp_t)___GFP_WRITE)
-#define __GFP_HARDWALL ((__force gfp_t)___GFP_HARDWALL)
-#define __GFP_THISNODE ((__force gfp_t)___GFP_THISNODE)
-#define __GFP_ACCOUNT ((__force gfp_t)___GFP_ACCOUNT)
-
-/**
- * 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.
- *
- * %__GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is
- * high priority. Users are typically interrupt handlers. This may be
- * used in conjunction with %__GFP_HIGH
- *
- * %__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_ATOMIC ((__force gfp_t)___GFP_ATOMIC)
-#define __GFP_HIGH ((__force gfp_t)___GFP_HIGH)
-#define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC)
-#define __GFP_NOMEMALLOC ((__force gfp_t)___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
- *
- * %__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 else where. 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.
- * 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.
- * Using this flag for costly allocations is _highly_ discouraged.
- */
-#define __GFP_IO ((__force gfp_t)___GFP_IO)
-#define __GFP_FS ((__force gfp_t)___GFP_FS)
-#define __GFP_DIRECT_RECLAIM ((__force gfp_t)___GFP_DIRECT_RECLAIM) /* Caller can reclaim */
-#define __GFP_KSWAPD_RECLAIM ((__force gfp_t)___GFP_KSWAPD_RECLAIM) /* kswapd can wake */
-#define __GFP_RECLAIM ((__force gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM))
-#define __GFP_RETRY_MAYFAIL ((__force gfp_t)___GFP_RETRY_MAYFAIL)
-#define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
-#define __GFP_NORETRY ((__force gfp_t)___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
- * performace impact.
- *
- * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page allocation.
- * Only effective in HW_TAGS mode.
- *
- * %__GFP_SKIP_KASAN_POISON makes KASAN skip poisoning on page deallocation.
- * Typically, used for userspace pages. Only effective in HW_TAGS mode.
- */
-#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
-#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
-#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
-#define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS)
-#define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO)
-#define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON)
-#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON)
-
-/* Disable lockdep for GFP context tracking */
-#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
-
-/* Room for N __GFP_FOO bits */
-#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))
-#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
-
-/**
- * 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.
- *
- * %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 (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
-#define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
-#define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT)
-#define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM)
-#define GFP_NOIO (__GFP_RECLAIM)
-#define GFP_NOFS (__GFP_RECLAIM | __GFP_IO)
-#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 | \
- __GFP_SKIP_KASAN_POISON)
-#define GFP_TRANSHUGE_LIGHT ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
- __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
-#define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
-
-/* Convert GFP flags to their corresponding migrate type */
-#define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
-#define GFP_MOVABLE_SHIFT 3
-
static inline int gfp_migratetype(const gfp_t gfp_flags)
{
VM_WARN_ON((gfp_flags & GFP_MOVABLE_MASK) == GFP_MOVABLE_MASK);
diff --git a/include/linux/gfp_flags.h b/include/linux/gfp_flags.h
new file mode 100644
index 000000000000..846cc8151340
--- /dev/null
+++ b/include/linux/gfp_flags.h
@@ -0,0 +1,338 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_GFP_FLAGS_H
+#define __LINUX_GFP_FLAGS_H
+
+/*
+ * In case of changes, please don't forget to update
+ * include/trace/events/mmflags.h and tools/perf/builtin-kmem.c
+ */
+
+/* Plain integer GFP bitmasks. Do not use this directly. */
+#define ___GFP_DMA 0x01u
+#define ___GFP_HIGHMEM 0x02u
+#define ___GFP_DMA32 0x04u
+#define ___GFP_MOVABLE 0x08u
+#define ___GFP_RECLAIMABLE 0x10u
+#define ___GFP_HIGH 0x20u
+#define ___GFP_IO 0x40u
+#define ___GFP_FS 0x80u
+#define ___GFP_ZERO 0x100u
+#define ___GFP_ATOMIC 0x200u
+#define ___GFP_DIRECT_RECLAIM 0x400u
+#define ___GFP_KSWAPD_RECLAIM 0x800u
+#define ___GFP_WRITE 0x1000u
+#define ___GFP_NOWARN 0x2000u
+#define ___GFP_RETRY_MAYFAIL 0x4000u
+#define ___GFP_NOFAIL 0x8000u
+#define ___GFP_NORETRY 0x10000u
+#define ___GFP_MEMALLOC 0x20000u
+#define ___GFP_COMP 0x40000u
+#define ___GFP_NOMEMALLOC 0x80000u
+#define ___GFP_HARDWALL 0x100000u
+#define ___GFP_THISNODE 0x200000u
+#define ___GFP_ACCOUNT 0x400000u
+#define ___GFP_ZEROTAGS 0x800000u
+#ifdef CONFIG_KASAN_HW_TAGS
+#define ___GFP_SKIP_ZERO 0x1000000u
+#define ___GFP_SKIP_KASAN_UNPOISON 0x2000000u
+#define ___GFP_SKIP_KASAN_POISON 0x4000000u
+#else
+#define ___GFP_SKIP_ZERO 0
+#define ___GFP_SKIP_KASAN_UNPOISON 0
+#define ___GFP_SKIP_KASAN_POISON 0
+#endif
+#ifdef CONFIG_LOCKDEP
+#define ___GFP_NOLOCKDEP 0x8000000u
+#else
+#define ___GFP_NOLOCKDEP 0
+#endif
+/* If the above are modified, __GFP_BITS_SHIFT may need updating */
+
+/*
+ * 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 ((__force gfp_t)___GFP_DMA)
+#define __GFP_HIGHMEM ((__force gfp_t)___GFP_HIGHMEM)
+#define __GFP_DMA32 ((__force gfp_t)___GFP_DMA32)
+#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
+#define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE)
+
+/**
+ * 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.
+ */
+#define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
+#define __GFP_WRITE ((__force gfp_t)___GFP_WRITE)
+#define __GFP_HARDWALL ((__force gfp_t)___GFP_HARDWALL)
+#define __GFP_THISNODE ((__force gfp_t)___GFP_THISNODE)
+#define __GFP_ACCOUNT ((__force gfp_t)___GFP_ACCOUNT)
+
+/**
+ * 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.
+ *
+ * %__GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is
+ * high priority. Users are typically interrupt handlers. This may be
+ * used in conjunction with %__GFP_HIGH
+ *
+ * %__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_ATOMIC ((__force gfp_t)___GFP_ATOMIC)
+#define __GFP_HIGH ((__force gfp_t)___GFP_HIGH)
+#define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC)
+#define __GFP_NOMEMALLOC ((__force gfp_t)___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
+ *
+ * %__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 else where. 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.
+ * 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.
+ * Using this flag for costly allocations is _highly_ discouraged.
+ */
+#define __GFP_IO ((__force gfp_t)___GFP_IO)
+#define __GFP_FS ((__force gfp_t)___GFP_FS)
+#define __GFP_DIRECT_RECLAIM ((__force gfp_t)___GFP_DIRECT_RECLAIM) /* Caller can reclaim */
+#define __GFP_KSWAPD_RECLAIM ((__force gfp_t)___GFP_KSWAPD_RECLAIM) /* kswapd can wake */
+#define __GFP_RECLAIM ((__force gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM))
+#define __GFP_RETRY_MAYFAIL ((__force gfp_t)___GFP_RETRY_MAYFAIL)
+#define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
+#define __GFP_NORETRY ((__force gfp_t)___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
+ * performace impact.
+ *
+ * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page allocation.
+ * Only effective in HW_TAGS mode.
+ *
+ * %__GFP_SKIP_KASAN_POISON makes KASAN skip poisoning on page deallocation.
+ * Typically, used for userspace pages. Only effective in HW_TAGS mode.
+ */
+#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
+#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
+#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
+#define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS)
+#define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO)
+#define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON)
+#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON)
+
+/* Disable lockdep for GFP context tracking */
+#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
+
+/* Room for N __GFP_FOO bits */
+#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))
+#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
+
+/**
+ * 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.
+ *
+ * %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 (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
+#define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
+#define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT)
+#define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM)
+#define GFP_NOIO (__GFP_RECLAIM)
+#define GFP_NOFS (__GFP_RECLAIM | __GFP_IO)
+#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 | \
+ __GFP_SKIP_KASAN_POISON)
+#define GFP_TRANSHUGE_LIGHT ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
+ __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
+#define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
+
+/* Convert GFP flags to their corresponding migrate type */
+#define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
+#define GFP_MOVABLE_SHIFT 3
+
+#endif /* __LINUX_GFP_FLAGS_H */