mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-24 09:50:04 +00:00
![Huang Shijie](/assets/img/avatar_default.png)
Follow the kernel conventions, rename addr_in_gen_pool to gen_pool_has_addr. [sjhuang@iluvatar.ai: fix Documentation/ too] Link: http://lkml.kernel.org/r/20181229015914.5573-1-sjhuang@iluvatar.ai Link: http://lkml.kernel.org/r/20181228083950.20398-1-sjhuang@iluvatar.ai Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
144 lines
5.7 KiB
ReStructuredText
144 lines
5.7 KiB
ReStructuredText
The genalloc/genpool subsystem
|
|
==============================
|
|
|
|
There are a number of memory-allocation subsystems in the kernel, each
|
|
aimed at a specific need. Sometimes, however, a kernel developer needs to
|
|
implement a new allocator for a specific range of special-purpose memory;
|
|
often that memory is located on a device somewhere. The author of the
|
|
driver for that device can certainly write a little allocator to get the
|
|
job done, but that is the way to fill the kernel with dozens of poorly
|
|
tested allocators. Back in 2005, Jes Sorensen lifted one of those
|
|
allocators from the sym53c8xx_2 driver and posted_ it as a generic module
|
|
for the creation of ad hoc memory allocators. This code was merged
|
|
for the 2.6.13 release; it has been modified considerably since then.
|
|
|
|
.. _posted: https://lwn.net/Articles/125842/
|
|
|
|
Code using this allocator should include <linux/genalloc.h>. The action
|
|
begins with the creation of a pool using one of:
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_create
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: devm_gen_pool_create
|
|
|
|
A call to gen_pool_create() will create a pool. The granularity of
|
|
allocations is set with min_alloc_order; it is a log-base-2 number like
|
|
those used by the page allocator, but it refers to bytes rather than pages.
|
|
So, if min_alloc_order is passed as 3, then all allocations will be a
|
|
multiple of eight bytes. Increasing min_alloc_order decreases the memory
|
|
required to track the memory in the pool. The nid parameter specifies
|
|
which NUMA node should be used for the allocation of the housekeeping
|
|
structures; it can be -1 if the caller doesn't care.
|
|
|
|
The "managed" interface devm_gen_pool_create() ties the pool to a
|
|
specific device. Among other things, it will automatically clean up the
|
|
pool when the given device is destroyed.
|
|
|
|
A pool is shut down with:
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_destroy
|
|
|
|
It's worth noting that, if there are still allocations outstanding from the
|
|
given pool, this function will take the rather extreme step of invoking
|
|
BUG(), crashing the entire system. You have been warned.
|
|
|
|
A freshly created pool has no memory to allocate. It is fairly useless in
|
|
that state, so one of the first orders of business is usually to add memory
|
|
to the pool. That can be done with one of:
|
|
|
|
.. kernel-doc:: include/linux/genalloc.h
|
|
:functions: gen_pool_add
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_add_owner
|
|
|
|
A call to gen_pool_add() will place the size bytes of memory
|
|
starting at addr (in the kernel's virtual address space) into the given
|
|
pool, once again using nid as the node ID for ancillary memory allocations.
|
|
The gen_pool_add_virt() variant associates an explicit physical
|
|
address with the memory; this is only necessary if the pool will be used
|
|
for DMA allocations.
|
|
|
|
The functions for allocating memory from the pool (and putting it back)
|
|
are:
|
|
|
|
.. kernel-doc:: include/linux/genalloc.h
|
|
:functions: gen_pool_alloc
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_dma_alloc
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_free_owner
|
|
|
|
As one would expect, gen_pool_alloc() will allocate size< bytes
|
|
from the given pool. The gen_pool_dma_alloc() variant allocates
|
|
memory for use with DMA operations, returning the associated physical
|
|
address in the space pointed to by dma. This will only work if the memory
|
|
was added with gen_pool_add_virt(). Note that this function
|
|
departs from the usual genpool pattern of using unsigned long values to
|
|
represent kernel addresses; it returns a void * instead.
|
|
|
|
That all seems relatively simple; indeed, some developers clearly found it
|
|
to be too simple. After all, the interface above provides no control over
|
|
how the allocation functions choose which specific piece of memory to
|
|
return. If that sort of control is needed, the following functions will be
|
|
of interest:
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_alloc_algo_owner
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_set_algo
|
|
|
|
Allocations with gen_pool_alloc_algo() specify an algorithm to be
|
|
used to choose the memory to be allocated; the default algorithm can be set
|
|
with gen_pool_set_algo(). The data value is passed to the
|
|
algorithm; most ignore it, but it is occasionally needed. One can,
|
|
naturally, write a special-purpose algorithm, but there is a fair set
|
|
already available:
|
|
|
|
- gen_pool_first_fit is a simple first-fit allocator; this is the default
|
|
algorithm if none other has been specified.
|
|
|
|
- gen_pool_first_fit_align forces the allocation to have a specific
|
|
alignment (passed via data in a genpool_data_align structure).
|
|
|
|
- gen_pool_first_fit_order_align aligns the allocation to the order of the
|
|
size. A 60-byte allocation will thus be 64-byte aligned, for example.
|
|
|
|
- gen_pool_best_fit, as one would expect, is a simple best-fit allocator.
|
|
|
|
- gen_pool_fixed_alloc allocates at a specific offset (passed in a
|
|
genpool_data_fixed structure via the data parameter) within the pool.
|
|
If the indicated memory is not available the allocation fails.
|
|
|
|
There is a handful of other functions, mostly for purposes like querying
|
|
the space available in the pool or iterating through chunks of memory.
|
|
Most users, however, should not need much beyond what has been described
|
|
above. With luck, wider awareness of this module will help to prevent the
|
|
writing of special-purpose memory allocators in the future.
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_virt_to_phys
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_for_each_chunk
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_has_addr
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_avail
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_size
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: gen_pool_get
|
|
|
|
.. kernel-doc:: lib/genalloc.c
|
|
:functions: of_gen_pool_get
|