[PATCH v3 0/7] memory management documentation updates

[PATCH v3 0/7] memory management documentation updates

[Mike Rapoport]

Hi,

Here are several updates to the mm documentation.

Aside from really minor changes in the first three patches, the updates
are:

* move the documentation of kstrdup and friends to "String Manipulation"
  section
* split memory management API into a separate .rst file
* adjust formating of the GFP flags description and include it in the
  reference documentation.

v3 changes:
* Use Matthew's wording of intro paragraph in the GFP flags section
* Change "Common Combinations" to "Useful GFP flag combinations"

v2 changes:
* move get_user_pages_fast documentation to "User Space Memory Access" as
  suggested by Matthew
* more elaborate changelog for the fifth patch


Mike Rapoport (7):
  mm/util: make strndup_user description a kernel-doc comment
  mm/util: add kernel-doc for kvfree
  docs/core-api: kill trailing whitespace in kernel-api.rst
  docs/core-api: move *{str,mem}dup* to "String Manipulation"
  docs/core-api: split memory management API to a separate file
  docs/mm: make GFP flags descriptions usable as kernel-doc
  docs/core-api: mm-api: add section about GFP flags

 Documentation/core-api/index.rst      |   1 +
 Documentation/core-api/kernel-api.rst |  59 +------
 Documentation/core-api/mm-api.rst     |  78 +++++++++
 include/linux/gfp.h                   | 291 ++++++++++++++++++----------------
 mm/util.c                             |   9 +-
 5 files changed, 245 insertions(+), 193 deletions(-)
 create mode 100644 Documentation/core-api/mm-api.rst

-- 
2.7.4

[PATCH v3 1/7] mm/util: make strndup_user description a kernel-doc comment

[Mike Rapoport]

The description of the strndup_user function misses '*' character at the
beginning of the comment to be proper kernel-doc. Add the missing
character.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 mm/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 3351659..6809014 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -196,7 +196,7 @@ void *vmemdup_user(const void __user *src, size_t len)
 }
 EXPORT_SYMBOL(vmemdup_user);
 
-/*
+/**
  * strndup_user - duplicate an existing string from user space
  * @s: The string to duplicate
  * @n: Maximum number of bytes to copy, including the trailing NUL.
-- 
2.7.4

[PATCH v3 2/7] mm/util: add kernel-doc for kvfree

[Mike Rapoport]

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 mm/util.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/util.c b/mm/util.c
index 6809014..d2890a4 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -434,6 +434,13 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
 }
 EXPORT_SYMBOL(kvmalloc_node);
 
+/**
+ * kvfree - free memory allocated with kvmalloc
+ * @addr: pointer returned by kvmalloc
+ *
+ * If the memory is allocated from vmalloc area it is freed with vfree().
+ * Otherwise kfree() is used.
+ */
 void kvfree(const void *addr)
 {
 	if (is_vmalloc_addr(addr))
-- 
2.7.4

[PATCH v3 3/7] docs/core-api: kill trailing whitespace in kernel-api.rst

[Mike Rapoport]

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 Documentation/core-api/kernel-api.rst | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
index 76fe2d0f..25e9496 100644
--- a/Documentation/core-api/kernel-api.rst
+++ b/Documentation/core-api/kernel-api.rst
@@ -437,4 +437,3 @@ Read-Copy Update (RCU)
 .. kernel-doc:: include/linux/rcu_sync.h
 
 .. kernel-doc:: kernel/rcu/sync.c
-
-- 
2.7.4

[PATCH v3 4/7] docs/core-api: move *{str,mem}dup* to "String Manipulation"

[Mike Rapoport]

The string and memory duplication routines fit better to the "String
Manipulation" section than to "The SLAB Cache".

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 Documentation/core-api/kernel-api.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
index 25e9496..39f1460 100644
--- a/Documentation/core-api/kernel-api.rst
+++ b/Documentation/core-api/kernel-api.rst
@@ -39,6 +39,10 @@ String Manipulation
 .. kernel-doc:: lib/string.c
    :export:
 
+.. kernel-doc:: mm/util.c
+   :functions: kstrdup kstrdup_const kstrndup kmemdup kmemdup_nul memdup_user
+               vmemdup_user strndup_user memdup_user_nul
+
 Basic Kernel Library Functions
 ==============================
 
@@ -168,7 +172,7 @@ The Slab Cache
    :export:
 
 .. kernel-doc:: mm/util.c
-   :export:
+   :functions: kfree_const kvmalloc_node kvfree get_user_pages_fast
 
 User Space Memory Access
 ------------------------
-- 
2.7.4

[PATCH v3 5/7] docs/core-api: split memory management API to a separate file

[Mike Rapoport]

This is basically copy-paste of the memory management section from
kernel-api.rst with some minor adjustments:

* The "User Space Memory Access" is moved to the beginning
* The get_user_pages_fast reference is now a part of "User Space Memory
  Access"
* And, of course, headings are adjusted with section being promoted to
  chapters

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 Documentation/core-api/index.rst      |  1 +
 Documentation/core-api/kernel-api.rst | 54 ---------------------------------
 Documentation/core-api/mm-api.rst     | 57 +++++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 54 deletions(-)
 create mode 100644 Documentation/core-api/mm-api.rst

diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index 989c97c..cdc2020 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -27,6 +27,7 @@ Core utilities
    errseq
    printk-formats
    circular-buffers
+   mm-api
    gfp_mask-from-fs-io
    timekeeping
 
diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
index 39f1460..3431337 100644
--- a/Documentation/core-api/kernel-api.rst
+++ b/Documentation/core-api/kernel-api.rst
@@ -159,60 +159,6 @@ UUID/GUID
 .. kernel-doc:: lib/uuid.c
    :export:
 
-Memory Management in Linux
-==========================
-
-The Slab Cache
---------------
-
-.. kernel-doc:: include/linux/slab.h
-   :internal:
-
-.. kernel-doc:: mm/slab.c
-   :export:
-
-.. kernel-doc:: mm/util.c
-   :functions: kfree_const kvmalloc_node kvfree get_user_pages_fast
-
-User Space Memory Access
-------------------------
-
-.. kernel-doc:: arch/x86/include/asm/uaccess.h
-   :internal:
-
-.. kernel-doc:: arch/x86/lib/usercopy_32.c
-   :export:
-
-More Memory Management Functions
---------------------------------
-
-.. kernel-doc:: mm/readahead.c
-   :export:
-
-.. kernel-doc:: mm/filemap.c
-   :export:
-
-.. kernel-doc:: mm/memory.c
-   :export:
-
-.. kernel-doc:: mm/vmalloc.c
-   :export:
-
-.. kernel-doc:: mm/page_alloc.c
-   :internal:
-
-.. kernel-doc:: mm/mempool.c
-   :export:
-
-.. kernel-doc:: mm/dmapool.c
-   :export:
-
-.. kernel-doc:: mm/page-writeback.c
-   :export:
-
-.. kernel-doc:: mm/truncate.c
-   :export:
-
 Kernel IPC facilities
 =====================
 
diff --git a/Documentation/core-api/mm-api.rst b/Documentation/core-api/mm-api.rst
new file mode 100644
index 0000000..b5913aa
--- /dev/null
+++ b/Documentation/core-api/mm-api.rst
@@ -0,0 +1,57 @@
+======================
+Memory Management APIs
+======================
+
+User Space Memory Access
+========================
+
+.. kernel-doc:: arch/x86/include/asm/uaccess.h
+   :internal:
+
+.. kernel-doc:: arch/x86/lib/usercopy_32.c
+   :export:
+
+.. kernel-doc:: mm/util.c
+   :functions: get_user_pages_fast
+
+The Slab Cache
+==============
+
+.. kernel-doc:: include/linux/slab.h
+   :internal:
+
+.. kernel-doc:: mm/slab.c
+   :export:
+
+.. kernel-doc:: mm/util.c
+   :functions: kfree_const kvmalloc_node kvfree
+
+More Memory Management Functions
+================================
+
+.. kernel-doc:: mm/readahead.c
+   :export:
+
+.. kernel-doc:: mm/filemap.c
+   :export:
+
+.. kernel-doc:: mm/memory.c
+   :export:
+
+.. kernel-doc:: mm/vmalloc.c
+   :export:
+
+.. kernel-doc:: mm/page_alloc.c
+   :internal:
+
+.. kernel-doc:: mm/mempool.c
+   :export:
+
+.. kernel-doc:: mm/dmapool.c
+   :export:
+
+.. kernel-doc:: mm/page-writeback.c
+   :export:
+
+.. kernel-doc:: mm/truncate.c
+   :export:
-- 
2.7.4

[PATCH v3 6/7] docs/mm: make GFP flags descriptions usable as kernel-doc

[Mike Rapoport]

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

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 include/linux/gfp.h | 291 +++++++++++++++++++++++++++-------------------------
 1 file changed, 154 insertions(+), 137 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index a6afcec..24bcc5ee 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -59,29 +59,32 @@ struct vm_area_struct;
 #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_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_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_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_HARDWALL enforces the cpuset memory allocation policy.
  *
- * __GFP_THISNODE forces the allocation to be satisified from the requested
- *   node with no fallbacks or placement policy enforcements.
+ * %__GFP_THISNODE forces the allocation to be satisified from the requested
+ * 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_WRITE	((__force gfp_t)___GFP_WRITE)
@@ -89,54 +92,60 @@ struct vm_area_struct;
 #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_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_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).
+ * %__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).
  *
- * __GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves.
- *   This takes precedence over the __GFP_MEMALLOC flag if both are set.
+ * %__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
+ * ~~~~~~~~~~~~~~~~~
  *
- * __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
- *   allocator recursing into the filesystem which might already be holding
- *   locks.
+ * %__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_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_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.
+ * %__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).
+ * 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
@@ -144,40 +153,40 @@ struct vm_area_struct;
  * 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.
+ * %__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)
@@ -188,14 +197,17 @@ struct vm_area_struct;
 #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_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_COMP	((__force gfp_t)___GFP_COMP)
@@ -208,66 +220,71 @@ struct vm_area_struct;
 #define __GFP_BITS_SHIFT (23 + 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"
- *
- * 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.
- *
- * 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.
+ * %__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"
+ *
+ * %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.
+ *
+ * %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)
-- 
2.7.4

Re: [PATCH v3 6/7] docs/mm: make GFP flags descriptions usable as kernel-doc

[Jonathan Corbet]

On Thu, 26 Jul 2018 20:32:39 +0300
Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:

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

So I think this is a great thing to do.  Adding cross references from
places where GFP flags are expected would be even better.  I do have one
little concern, though...

> - * __GFP_MOVABLE (also a zone modifier) indicates that the page can be
> - *   moved by page migration during memory compaction or can be reclaimed.
> + * %__GFP_MOVABLE (also a zone modifier) indicates that the page can be
> + * moved by page migration during memory compaction or can be reclaimed.

There are Certain Developers who get rather bent out of shape when they
feel that excessive markup is degrading the readability of the plain-text
documentation.  I have a suspicion that all of these % signs might turn
out to be one of those places.  People have been trained to expect them in
function documentation, but that's not quite what we have here.

I won't insist on this, but I would suggest that, in this particular case,
it might be better for that markup to come out.

Then we have the same old question of who applies these.  I'd love to have
an ack from somebody who can speak for mm - or a statement that these will
go through another tree.  Preferably quickly so that this stuff can get
in through the upcoming merge window.

Thanks,

jon

Re: [PATCH v3 6/7] docs/mm: make GFP flags descriptions usable as kernel-doc

[Mike Rapoport]

On Thu, Jul 26, 2018 at 04:08:25PM -0600, Jonathan Corbet wrote:
> On Thu, 26 Jul 2018 20:32:39 +0300
> Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> 
> > This patch adds DOC: headings for GFP flag descriptions and adjusts the
> > formatting to fit sphinx expectations of paragraphs.
> 
> So I think this is a great thing to do.  Adding cross references from
> places where GFP flags are expected would be even better.  I do have one
> little concern, though...
> 
> > - * __GFP_MOVABLE (also a zone modifier) indicates that the page can be
> > - *   moved by page migration during memory compaction or can be reclaimed.
> > + * %__GFP_MOVABLE (also a zone modifier) indicates that the page can be
> > + * moved by page migration during memory compaction or can be reclaimed.
> 
> There are Certain Developers who get rather bent out of shape when they
> feel that excessive markup is degrading the readability of the plain-text
> documentation.  I have a suspicion that all of these % signs might turn
> out to be one of those places.  People have been trained to expect them in
> function documentation, but that's not quite what we have here.
> 
> I won't insist on this, but I would suggest that, in this particular case,
> it might be better for that markup to come out.

No problem with removing % signs, but the whitespace changes are necessary,
otherwise the generated html gets weird.
 
> Then we have the same old question of who applies these.  I'd love to have
> an ack from somebody who can speak for mm - or a statement that these will
> go through another tree.  Preferably quickly so that this stuff can get
> in through the upcoming merge window.

> Thanks,
> 
> jon
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v3 6/7] docs/mm: make GFP flags descriptions usable as kernel-doc

[Jonathan Corbet]

On Sat, 28 Jul 2018 00:27:21 +0300
Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:

> > I won't insist on this, but I would suggest that, in this particular case,
> > it might be better for that markup to come out.  
> 
> No problem with removing % signs, but the whitespace changes are necessary,
> otherwise the generated html gets weird.

The whitespace changes are fine - it's really just the % markup I was
commenting on.

Thanks,

jon

[PATCH v3 7/7] docs/core-api: mm-api: add section about GFP flags

[Mike Rapoport]

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 Documentation/core-api/mm-api.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Documentation/core-api/mm-api.rst b/Documentation/core-api/mm-api.rst
index b5913aa..46ae353 100644
--- a/Documentation/core-api/mm-api.rst
+++ b/Documentation/core-api/mm-api.rst
@@ -14,6 +14,27 @@ User Space Memory Access
 .. kernel-doc:: mm/util.c
    :functions: get_user_pages_fast
 
+Memory Allocation Controls
+==========================
+
+Functions which need to allocate memory often use GFP flags to express
+how that memory should be allocated. The GFP acronym stands for "get
+free pages", the underlying memory allocation function. Not every GFP
+flag is allowed to every function which may allocate memory. Most
+users will want to use a plain ``GFP_KERNEL``.
+
+.. kernel-doc:: include/linux/gfp.h
+   :doc: Page mobility and placement hints
+
+.. kernel-doc:: include/linux/gfp.h
+   :doc: Watermark modifiers
+
+.. kernel-doc:: include/linux/gfp.h
+   :doc: Reclaim modifiers
+
+.. kernel-doc:: include/linux/gfp.h
+   :doc: Common combinations
+
 The Slab Cache
 ==============
 
-- 
2.7.4