[PATCH 1/2] docs/core-api: memory-allocation: add k[mz]alloc_obj() and clarify kmalloc

[Mike Rapoport (Microsoft)]

Since v7.0 the most used memory allocation function is kzalloc_obj().

Update hte memory-allocation guide to describe k[mz]alloc_obj() family
and make kzalloc_obj() the first answer to "How should I allocate
memory?" question.

While on it, clarify description of kmalloc() size limitations.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 Documentation/core-api/memory-allocation.rst | 30 +++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 0f19dd5243239..8ecfa4d35f4f5 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -19,6 +19,12 @@ Diversity of the allocation APIs combined with the numerous GFP flags
 makes the question "How should I allocate memory?" not that easy to
 answer, although very likely you should use
 
+::
+
+  kzalloc_obj(<VAR_OR_TYPE>);
+
+or
+
 ::
 
   kzalloc(<size>, GFP_KERNEL);
@@ -139,10 +145,13 @@ allocate memory for an array, there are kmalloc_array() and kcalloc()
 helpers. The helpers struct_size(), array_size() and array3_size() can
 be used to safely calculate object sizes without overflowing.
 
-The maximal size of a chunk that can be allocated with `kmalloc` is
-limited. The actual limit depends on the hardware and the kernel
-configuration, but it is a good practice to use `kmalloc` for objects
-smaller than page size.
+Since 7.0 there are type aware kmalloc-family helpers that let you safely and
+conveniently allocate a single object or arrays of objects with kzalloc_obj()
+and kmalloc_obj() and their array versions kzalloc_objs() and
+kmalloc_objs(). These helpers only need the type of the object that should be
+allocated and the count of elements in the array for the array versions.
+
+As of v7.2, vast majority of the memory allocations use kzalloc_obj().
 
 The address of a chunk allocated with `kmalloc` is aligned to at least
 ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the
@@ -154,9 +163,16 @@ Chunks allocated with kmalloc() can be resized with krealloc(). Similarly
 to kmalloc_array(): a helper for resizing arrays is provided in the form of
 krealloc_array().
 
-For large allocations you can use vmalloc() and vzalloc(), or directly
-request pages from the page allocator. The memory allocated by `vmalloc`
-and related functions is not physically contiguous.
+`kmalloc` always allocates physically contiguous memory and the maximal size of
+a chunk that can be allocated with `kmalloc` is limited by `MAX_ORDER`, the
+same limit also applies to the page allocator.
+
+Internally, slab allocator differentiates allocations of different orders and
+delegates larger allocations to the page allocator, but for the users of
+`kmalloc` family it is entirely transparent.
+
+For large allocations that do not require physically contiguous memory you can
+use vmalloc() and vzalloc() family.
 
 If you are not sure whether the allocation size is too large for
 `kmalloc`, it is possible to use kvmalloc() and its derivatives. It will

-- 
2.53.0