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.com Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Andrew 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Rapoport
Linus Torvalds
parent
41f35b395c
commit
263fade51f
1 changed files with 140 additions and 123 deletions
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@ -59,29 +59,32 @@ struct vm_area_struct;
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#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
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#define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE)
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/*
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/**
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* DOC: Page mobility and placement hints
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*
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* Page mobility and placement hints
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* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*
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* These flags provide hints about how mobile the page is. Pages with similar
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* mobility are placed within the same pageblocks to minimise problems due
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* to external fragmentation.
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*
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* __GFP_MOVABLE (also a zone modifier) indicates that the page can be
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* %__GFP_MOVABLE (also a zone modifier) indicates that the page can be
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* moved by page migration during memory compaction or can be reclaimed.
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*
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* __GFP_RECLAIMABLE is used for slab allocations that specify
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* %__GFP_RECLAIMABLE is used for slab allocations that specify
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* SLAB_RECLAIM_ACCOUNT and whose pages can be freed via shrinkers.
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*
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* __GFP_WRITE indicates the caller intends to dirty the page. Where possible,
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* %__GFP_WRITE indicates the caller intends to dirty the page. Where possible,
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* these pages will be spread between local zones to avoid all the dirty
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* pages being in one zone (fair zone allocation policy).
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*
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* __GFP_HARDWALL enforces the cpuset memory allocation policy.
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* %__GFP_HARDWALL enforces the cpuset memory allocation policy.
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*
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* __GFP_THISNODE forces the allocation to be satisified from the requested
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* %__GFP_THISNODE forces the allocation to be satisified from the requested
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* node with no fallbacks or placement policy enforcements.
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*
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* __GFP_ACCOUNT causes the allocation to be accounted to kmemcg.
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* %__GFP_ACCOUNT causes the allocation to be accounted to kmemcg.
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*/
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#define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
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#define __GFP_WRITE ((__force gfp_t)___GFP_WRITE)
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@ -89,54 +92,60 @@ struct vm_area_struct;
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#define __GFP_THISNODE ((__force gfp_t)___GFP_THISNODE)
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#define __GFP_ACCOUNT ((__force gfp_t)___GFP_ACCOUNT)
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/*
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* Watermark modifiers -- controls access to emergency reserves
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/**
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* DOC: Watermark modifiers
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*
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* __GFP_HIGH indicates that the caller is high-priority and that granting
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* Watermark modifiers -- controls access to emergency reserves
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* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*
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* %__GFP_HIGH 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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*
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* __GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is
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* %__GFP_ATOMIC 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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* used in conjunction with %__GFP_HIGH
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*
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* __GFP_MEMALLOC allows access to all memory. This should only be used when
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* %__GFP_MEMALLOC allows access to all memory. This should only be used when
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* the caller guarantees the allocation will allow more memory to be freed
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* very shortly e.g. process exiting or swapping. Users either should
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* be the MM or co-ordinating closely with the VM (e.g. swap over NFS).
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*
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* __GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves.
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* This takes precedence over the __GFP_MEMALLOC flag if both are set.
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* %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves.
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* This takes precedence over the %__GFP_MEMALLOC flag if both are set.
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*/
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#define __GFP_ATOMIC ((__force gfp_t)___GFP_ATOMIC)
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#define __GFP_HIGH ((__force gfp_t)___GFP_HIGH)
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#define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC)
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#define __GFP_NOMEMALLOC ((__force gfp_t)___GFP_NOMEMALLOC)
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/*
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/**
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* DOC: Reclaim modifiers
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*
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* Reclaim modifiers
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* ~~~~~~~~~~~~~~~~~
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*
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* __GFP_IO can start physical IO.
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* %__GFP_IO can start physical IO.
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*
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* __GFP_FS can call down to the low-level FS. Clearing the flag avoids the
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* %__GFP_FS 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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*
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* __GFP_DIRECT_RECLAIM indicates that the caller may enter direct reclaim.
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* %__GFP_DIRECT_RECLAIM 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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*
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* __GFP_KSWAPD_RECLAIM indicates that the caller wants to wake kswapd when
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* %__GFP_KSWAPD_RECLAIM 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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*
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* __GFP_RECLAIM is shorthand to allow/forbid both direct and kswapd reclaim.
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* %__GFP_RECLAIM is shorthand to allow/forbid both direct and kswapd reclaim.
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*
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* The default allocator behavior depends on the request size. We have a concept
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* of so called costly allocations (with order > PAGE_ALLOC_COSTLY_ORDER).
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* of so called costly allocations (with order > %PAGE_ALLOC_COSTLY_ORDER).
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* !costly allocations are too essential to fail so they are implicitly
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* non-failing by default (with some exceptions like OOM victims might fail so
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* the caller still has to check for failures) while costly requests try to be
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@ -144,20 +153,20 @@ struct vm_area_struct;
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* The following three modifiers might be used to override some of these
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* implicit rules
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*
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* __GFP_NORETRY: The VM implementation will try only very lightweight
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* %__GFP_NORETRY: The VM implementation will try only very lightweight
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* memory direct reclaim to get some memory under memory pressure (thus
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* it can sleep). It will avoid disruptive actions like OOM killer. The
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* caller must handle the failure which is quite likely to happen under
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* heavy memory pressure. The flag is suitable when failure can easily be
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* handled at small cost, such as reduced throughput
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*
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* __GFP_RETRY_MAYFAIL: The VM implementation will retry memory reclaim
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* %__GFP_RETRY_MAYFAIL: The VM implementation will retry memory reclaim
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* procedures that have previously failed if there is some indication
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* that progress has been made else where. It can wait for other
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* tasks to attempt high level approaches to freeing memory such as
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* compaction (which removes fragmentation) and page-out.
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* There is still a definite limit to the number of retries, but it is
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* a larger limit than with __GFP_NORETRY.
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* a larger limit than with %__GFP_NORETRY.
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* Allocations with this flag may fail, but only when there is
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* genuinely little unused memory. While these allocations do not
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* directly trigger the OOM killer, their failure indicates that
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@ -169,7 +178,7 @@ struct vm_area_struct;
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* free some non-essential memory, doing so could benefit the system
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* as a whole.
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*
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* __GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
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* %__GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
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* cannot handle allocation failures. The allocation could block
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* indefinitely but will never return with failure. Testing for
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* failure is pointless.
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@ -188,14 +197,17 @@ struct vm_area_struct;
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#define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
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#define __GFP_NORETRY ((__force gfp_t)___GFP_NORETRY)
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/*
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/**
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* DOC: Action modifiers
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*
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* Action modifiers
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* ~~~~~~~~~~~~~~~~
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*
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* __GFP_NOWARN suppresses allocation failure reports.
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* %__GFP_NOWARN suppresses allocation failure reports.
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*
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* __GFP_COMP address compound page metadata.
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* %__GFP_COMP address compound page metadata.
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*
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* __GFP_ZERO returns a zeroed page on success.
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* %__GFP_ZERO returns a zeroed page on success.
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*/
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#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
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#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
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@ -208,63 +220,68 @@ struct vm_area_struct;
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#define __GFP_BITS_SHIFT (23 + IS_ENABLED(CONFIG_LOCKDEP))
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#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
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/*
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/**
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* DOC: Useful GFP flag combinations
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*
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* Useful GFP flag combinations
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* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*
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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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* __GFP_FOO flags as necessary.
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* %__GFP_FOO flags as necessary.
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*
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* GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower
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* %GFP_ATOMIC 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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*
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* GFP_KERNEL 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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* %GFP_KERNEL 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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*
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* GFP_KERNEL_ACCOUNT is the same as GFP_KERNEL, except the allocation is
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* %GFP_KERNEL_ACCOUNT is the same as GFP_KERNEL, except the allocation is
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* accounted to kmemcg.
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*
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* GFP_NOWAIT is for kernel allocations that should not stall for direct
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* %GFP_NOWAIT 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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*
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* GFP_NOIO will use direct reclaim to discard clean pages or slab pages
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* %GFP_NOIO 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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*
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* GFP_NOFS will use direct reclaim but will not use any filesystem interfaces.
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* %GFP_NOFS 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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*
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* GFP_USER is for userspace allocations that also need to be directly
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* %GFP_USER 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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*
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* GFP_DMA exists for historical reasons and should be avoided where possible.
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* %GFP_DMA 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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* 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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* 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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*
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* GFP_DMA32 is similar to GFP_DMA except that the caller requires a 32-bit
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* %GFP_DMA32 is similar to %GFP_DMA except that the caller requires a 32-bit
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* address.
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*
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* GFP_HIGHUSER is for userspace allocations that may be mapped to userspace,
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* %GFP_HIGHUSER 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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*
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* GFP_HIGHUSER_MOVABLE is for userspace allocations that the kernel does not
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* %GFP_HIGHUSER_MOVABLE is for userspace allocations that the kernel does not
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* need direct access to but can use kmap() when access is required. They
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* are expected to be movable via page reclaim or page migration. Typically,
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* pages on the LRU would also be allocated with GFP_HIGHUSER_MOVABLE.
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* pages on the LRU would also be allocated with %GFP_HIGHUSER_MOVABLE.
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*
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* GFP_TRANSHUGE and GFP_TRANSHUGE_LIGHT are used for THP allocations. They are
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* compound allocations that will generally fail quickly if memory is not
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* %GFP_TRANSHUGE and %GFP_TRANSHUGE_LIGHT are used for THP allocations. They
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* are compound allocations that will generally fail quickly if memory is not
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* available and will not wake kswapd/kcompactd on failure. The _LIGHT
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* version does not attempt reclaim/compaction at all and is by default used
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* in page fault path, while the non-light is used by khugepaged.
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