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Commit 263fade5 authored by Mike Rapoport's avatar Mike Rapoport Committed by Linus Torvalds
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docs/mm: make GFP flags descriptions usable as kernel-doc 

This patch adds DOC: headings for GFP flag descriptions and adjusts the
formatting to fit sphinx expectations of paragraphs.

Link: http://lkml.kernel.org/r/1532626360-16650-7-git-send-email-rppt@linux.vnet.ibm.comSigned-off-by: default avatarMike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 41f35b39
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Showing with 154 additions and 137 deletions
include/linux/gfp.h
View file @ 263fade5
...@@ -59,29 +59,32 @@ struct vm_area_struct; ...@@ -59,29 +59,32 @@ struct vm_area_struct;
#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */ #define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
#define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE) #define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE)
/* /**
* DOC: Page mobility and placement hints
*
* Page mobility and placement hints * Page mobility and placement hints
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* *
* These flags provide hints about how mobile the page is. Pages with similar * These flags provide hints about how mobile the page is. Pages with similar
* mobility are placed within the same pageblocks to minimise problems due * mobility are placed within the same pageblocks to minimise problems due
* to external fragmentation. * to external fragmentation.
* *
* __GFP_MOVABLE (also a zone modifier) indicates that the page can be * %__GFP_MOVABLE (also a zone modifier) indicates that the page can be
* moved by page migration during memory compaction or can be reclaimed. * moved by page migration during memory compaction or can be reclaimed.
* *
* __GFP_RECLAIMABLE is used for slab allocations that specify * %__GFP_RECLAIMABLE is used for slab allocations that specify
* SLAB_RECLAIM_ACCOUNT and whose pages can be freed via shrinkers. * SLAB_RECLAIM_ACCOUNT and whose pages can be freed via shrinkers.
* *
* __GFP_WRITE indicates the caller intends to dirty the page. Where possible, * %__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 * these pages will be spread between local zones to avoid all the dirty
* pages being in one zone (fair zone allocation policy). * pages being in one zone (fair zone allocation policy).
* *
* __GFP_HARDWALL enforces the cpuset memory allocation policy. * %__GFP_HARDWALL enforces the cpuset memory allocation policy.
* *
* __GFP_THISNODE forces the allocation to be satisified from the requested * %__GFP_THISNODE forces the allocation to be satisified from the requested
* node with no fallbacks or placement policy enforcements. * node with no fallbacks or placement policy enforcements.
* *
* __GFP_ACCOUNT causes the allocation to be accounted to kmemcg. * %__GFP_ACCOUNT causes the allocation to be accounted to kmemcg.
*/ */
#define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE) #define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
#define __GFP_WRITE ((__force gfp_t)___GFP_WRITE) #define __GFP_WRITE ((__force gfp_t)___GFP_WRITE)
...@@ -89,54 +92,60 @@ struct vm_area_struct; ...@@ -89,54 +92,60 @@ struct vm_area_struct;
#define __GFP_THISNODE ((__force gfp_t)___GFP_THISNODE) #define __GFP_THISNODE ((__force gfp_t)___GFP_THISNODE)
#define __GFP_ACCOUNT ((__force gfp_t)___GFP_ACCOUNT) #define __GFP_ACCOUNT ((__force gfp_t)___GFP_ACCOUNT)
/* /**
* DOC: Watermark modifiers
*
* Watermark modifiers -- controls access to emergency reserves * Watermark modifiers -- controls access to emergency reserves
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* *
* __GFP_HIGH indicates that the caller is high-priority and that granting * %__GFP_HIGH indicates that the caller is high-priority and that granting
* the request is necessary before the system can make forward progress. * the request is necessary before the system can make forward progress.
* For example, creating an IO context to clean pages. * For example, creating an IO context to clean pages.
* *
* __GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is * %__GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is
* high priority. Users are typically interrupt handlers. This may be * high priority. Users are typically interrupt handlers. This may be
* used in conjunction with __GFP_HIGH * used in conjunction with %__GFP_HIGH
* *
* __GFP_MEMALLOC allows access to all memory. This should only be used when * %__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 * the caller guarantees the allocation will allow more memory to be freed
* very shortly e.g. process exiting or swapping. Users either should * 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). * be the MM or co-ordinating closely with the VM (e.g. swap over NFS).
* *
* __GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves.
* This takes precedence over the __GFP_MEMALLOC flag if both are set. * This takes precedence over the %__GFP_MEMALLOC flag if both are set.
*/ */
#define __GFP_ATOMIC ((__force gfp_t)___GFP_ATOMIC) #define __GFP_ATOMIC ((__force gfp_t)___GFP_ATOMIC)
#define __GFP_HIGH ((__force gfp_t)___GFP_HIGH) #define __GFP_HIGH ((__force gfp_t)___GFP_HIGH)
#define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC) #define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC)
#define __GFP_NOMEMALLOC ((__force gfp_t)___GFP_NOMEMALLOC) #define __GFP_NOMEMALLOC ((__force gfp_t)___GFP_NOMEMALLOC)
/* /**
* DOC: Reclaim modifiers
*
* Reclaim modifiers * Reclaim modifiers
* ~~~~~~~~~~~~~~~~~
* *
* __GFP_IO can start physical IO. * %__GFP_IO can start physical IO.
* *
* __GFP_FS can call down to the low-level FS. Clearing the flag avoids the * %__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 * allocator recursing into the filesystem which might already be holding
* locks. * locks.
* *
* __GFP_DIRECT_RECLAIM indicates that the caller may enter direct reclaim. * %__GFP_DIRECT_RECLAIM indicates that the caller may enter direct reclaim.
* This flag can be cleared to avoid unnecessary delays when a fallback * This flag can be cleared to avoid unnecessary delays when a fallback
* option is available. * option is available.
* *
* __GFP_KSWAPD_RECLAIM indicates that the caller wants to wake kswapd when * %__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 * 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 * 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 * options are available and the reclaim is likely to disrupt the system. The
* canonical example is THP allocation where a fallback is cheap but * canonical example is THP allocation where a fallback is cheap but
* reclaim/compaction may cause indirect stalls. * reclaim/compaction may cause indirect stalls.
* *
* __GFP_RECLAIM is shorthand to allow/forbid both direct and kswapd reclaim. * %__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 * The default allocator behavior depends on the request size. We have a concept
* of so called costly allocations (with order > PAGE_ALLOC_COSTLY_ORDER). * of so called costly allocations (with order > %PAGE_ALLOC_COSTLY_ORDER).
* !costly allocations are too essential to fail so they are implicitly * !costly allocations are too essential to fail so they are implicitly
* non-failing by default (with some exceptions like OOM victims might fail so * 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 * the caller still has to check for failures) while costly requests try to be
...@@ -144,20 +153,20 @@ struct vm_area_struct; ...@@ -144,20 +153,20 @@ struct vm_area_struct;
* The following three modifiers might be used to override some of these * The following three modifiers might be used to override some of these
* implicit rules * implicit rules
* *
* __GFP_NORETRY: The VM implementation will try only very lightweight * %__GFP_NORETRY: The VM implementation will try only very lightweight
* memory direct reclaim to get some memory under memory pressure (thus * memory direct reclaim to get some memory under memory pressure (thus
* it can sleep). It will avoid disruptive actions like OOM killer. The * it can sleep). It will avoid disruptive actions like OOM killer. The
* caller must handle the failure which is quite likely to happen under * caller must handle the failure which is quite likely to happen under
* heavy memory pressure. The flag is suitable when failure can easily be * heavy memory pressure. The flag is suitable when failure can easily be
* handled at small cost, such as reduced throughput * handled at small cost, such as reduced throughput
* *
* __GFP_RETRY_MAYFAIL: The VM implementation will retry memory reclaim * %__GFP_RETRY_MAYFAIL: The VM implementation will retry memory reclaim
* procedures that have previously failed if there is some indication * procedures that have previously failed if there is some indication
* that progress has been made else where. It can wait for other * that progress has been made else where. It can wait for other
* tasks to attempt high level approaches to freeing memory such as * tasks to attempt high level approaches to freeing memory such as
* compaction (which removes fragmentation) and page-out. * compaction (which removes fragmentation) and page-out.
* There is still a definite limit to the number of retries, but it is * There is still a definite limit to the number of retries, but it is
* a larger limit than with __GFP_NORETRY. * a larger limit than with %__GFP_NORETRY.
* Allocations with this flag may fail, but only when there is * Allocations with this flag may fail, but only when there is
* genuinely little unused memory. While these allocations do not * genuinely little unused memory. While these allocations do not
* directly trigger the OOM killer, their failure indicates that * directly trigger the OOM killer, their failure indicates that
...@@ -169,7 +178,7 @@ struct vm_area_struct; ...@@ -169,7 +178,7 @@ struct vm_area_struct;
* free some non-essential memory, doing so could benefit the system * free some non-essential memory, doing so could benefit the system
* as a whole. * as a whole.
* *
* __GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller * %__GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
* cannot handle allocation failures. The allocation could block * cannot handle allocation failures. The allocation could block
* indefinitely but will never return with failure. Testing for * indefinitely but will never return with failure. Testing for
* failure is pointless. * failure is pointless.
...@@ -188,14 +197,17 @@ struct vm_area_struct; ...@@ -188,14 +197,17 @@ struct vm_area_struct;
#define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL) #define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
#define __GFP_NORETRY ((__force gfp_t)___GFP_NORETRY) #define __GFP_NORETRY ((__force gfp_t)___GFP_NORETRY)
/* /**
* DOC: Action modifiers
*
* Action modifiers * Action modifiers
* ~~~~~~~~~~~~~~~~
* *
* __GFP_NOWARN suppresses allocation failure reports. * %__GFP_NOWARN suppresses allocation failure reports.
* *
* __GFP_COMP address compound page metadata. * %__GFP_COMP address compound page metadata.
* *
* __GFP_ZERO returns a zeroed page on success. * %__GFP_ZERO returns a zeroed page on success.
*/ */
#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN) #define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
#define __GFP_COMP ((__force gfp_t)___GFP_COMP) #define __GFP_COMP ((__force gfp_t)___GFP_COMP)
...@@ -208,63 +220,68 @@ struct vm_area_struct; ...@@ -208,63 +220,68 @@ struct vm_area_struct;
#define __GFP_BITS_SHIFT (23 + IS_ENABLED(CONFIG_LOCKDEP)) #define __GFP_BITS_SHIFT (23 + IS_ENABLED(CONFIG_LOCKDEP))
#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1)) #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 * Useful GFP flag combinations that are commonly used. It is recommended
* that subsystems start with one of these combinations and then set/clear * that subsystems start with one of these combinations and then set/clear
* __GFP_FOO flags as necessary. * %__GFP_FOO flags as necessary.
* *
* GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower * %GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower
* watermark is applied to allow access to "atomic reserves" * watermark is applied to allow access to "atomic reserves"
* *
* GFP_KERNEL is typical for kernel-internal allocations. The caller requires * %GFP_KERNEL is typical for kernel-internal allocations. The caller requires
* ZONE_NORMAL or a lower zone for direct access but can direct reclaim. * %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 * %GFP_KERNEL_ACCOUNT is the same as GFP_KERNEL, except the allocation is
* accounted to kmemcg. * accounted to kmemcg.
* *
* GFP_NOWAIT is for kernel allocations that should not stall for direct * %GFP_NOWAIT is for kernel allocations that should not stall for direct
* reclaim, start physical IO or use any filesystem callback. * reclaim, start physical IO or use any filesystem callback.
* *
* GFP_NOIO will use direct reclaim to discard clean pages or slab pages * %GFP_NOIO will use direct reclaim to discard clean pages or slab pages
* that do not require the starting of any physical IO. * that do not require the starting of any physical IO.
* Please try to avoid using this flag directly and instead use * Please try to avoid using this flag directly and instead use
* memalloc_noio_{save,restore} to mark the whole scope which cannot * memalloc_noio_{save,restore} to mark the whole scope which cannot
* perform any IO with a short explanation why. All allocation requests * perform any IO with a short explanation why. All allocation requests
* will inherit GFP_NOIO implicitly. * will inherit GFP_NOIO implicitly.
* *
* GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. * %GFP_NOFS will use direct reclaim but will not use any filesystem interfaces.
* Please try to avoid using this flag directly and instead use * Please try to avoid using this flag directly and instead use
* memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't * 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 * recurse into the FS layer with a short explanation why. All allocation
* requests will inherit GFP_NOFS implicitly. * requests will inherit GFP_NOFS implicitly.
* *
* GFP_USER is for userspace allocations that also need to be directly * %GFP_USER is for userspace allocations that also need to be directly
* accessibly by the kernel or hardware. It is typically used by hardware * accessibly by the kernel or hardware. It is typically used by hardware
* for buffers that are mapped to userspace (e.g. graphics) that hardware * for buffers that are mapped to userspace (e.g. graphics) that hardware
* still must DMA to. cpuset limits are enforced for these allocations. * still must DMA to. cpuset limits are enforced for these allocations.
* *
* GFP_DMA exists for historical reasons and should be avoided where possible. * %GFP_DMA exists for historical reasons and should be avoided where possible.
* The flags indicates that the caller requires that the lowest zone be * 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 * 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 * 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 * others use the flag to avoid lowmem reserves in %ZONE_DMA and treat the
* lowest zone as a type of emergency reserve. * lowest zone as a type of emergency reserve.
* *
* GFP_DMA32 is similar to GFP_DMA except that the caller requires a 32-bit * %GFP_DMA32 is similar to %GFP_DMA except that the caller requires a 32-bit
* address. * address.
* *
* GFP_HIGHUSER is for userspace allocations that may be mapped to userspace, * %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 * 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 * move once in use. An example may be a hardware allocation that maps
* data directly into userspace but has no addressing limitations. * data directly into userspace but has no addressing limitations.
* *
* GFP_HIGHUSER_MOVABLE is for userspace allocations that the kernel does not * %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 * 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, * are expected to be movable via page reclaim or page migration. Typically,
* pages on the LRU would also be allocated with GFP_HIGHUSER_MOVABLE. * 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 * %GFP_TRANSHUGE and %GFP_TRANSHUGE_LIGHT are used for THP allocations. They
* compound allocations that will generally fail quickly if memory is not * are compound allocations that will generally fail quickly if memory is not
* available and will not wake kswapd/kcompactd on failure. The _LIGHT * available and will not wake kswapd/kcompactd on failure. The _LIGHT
* version does not attempt reclaim/compaction at all and is by default used * 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. * in page fault path, while the non-light is used by khugepaged.
......
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