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Subject[PATCHv12 0/8] Contiguous Memory Allocator
Hello everyone,

This is yet another round of Contiguous Memory Allocator patches. Now I
focused mainly on the integration of CMA to DMA mapping subsystem on ARM
architecture. In this version I've tried to solve the issue of the
aliasing in coherent memory mapping that was present in earlier versions
of DMA mapping framework.

The proposed solution should be considered as a proof-of-concept. Right
now it doesn't support GFP_ATOMIC allocations. Support for them is on my
TODO list and will be implemented on top of the "ARM: DMA: steal memory
for DMA coherent mappings" patch by Russell King.

A few words for these who see CMA for the first time:

The Contiguous Memory Allocator (CMA) makes it possible for device
drivers to allocate big contiguous chunks of memory after the system
has booted.

The main difference from the similar frameworks is the fact that CMA
allows to transparently reuse memory region reserved for the big
chunk allocation as a system memory, so no memory is wasted when no
big chunk is allocated. Once the alloc request is issued, the
framework will migrate system pages to create a required big chunk of
physically contiguous memory.

For more information you can refer to nice LWN articles: and
as well as links to previous versions of the CMA framework.

The CMA framework has been initially developed by Michal Nazarewicz
at Samsung Poland R&D Center. Since version 9, I've taken over the
development, because Michal has left the company.

The current version of CMA is a set of helper functions for DMA mapping
framework that handles allocation of contiguous memory blocks. The
difference between this patchset and Kamezawa's alloc_contig_pages()

1. alloc_contig_pages() requires MAX_ORDER alignment of allocations
which may be unsuitable for embeded systems where a few MiBs are

Lack of the requirement on the alignment means that several threads
might try to access the same pageblock/page. To prevent this from
happening CMA uses a mutex so that only one allocating/releasing
function may run at one point.

2. CMA may use its own migratetype (MIGRATE_CMA) which behaves
similarly to ZONE_MOVABLE but can be put in arbitrary places.

This is required for us since we need to define two disjoint memory
ranges inside system RAM. (ie. in two memory banks (do not confuse
with nodes)).

3. alloc_contig_pages() scans memory in search for range that could be
migrated. CMA on the other hand maintains its own allocator to
decide where to allocate memory for device drivers and then tries
to migrate pages from that part if needed. This is not strictly
required but I somehow feel it might be faster.

The integration with ARM DMA-mapping subsystem is done on 2 levels.
During early boot memory reserved for contiguous areas are remapped with
2-level page tables. This enables us to change cache attributes of the
individual pages from such area on request. Then, DMA mapping subsystem
is updated to use dma_alloc_from_contiguous() call instead of
alloc_pages() and perform page attributes remapping.

Current version have been tested on Samsung S5PC110 based Goni machine
and s5p-fimc V4L2 driver. The driver itself uses videobuf2 dma-contig
memory allocator, which in turn relies on dma_alloc_coherent() from
DMA-mapping subsystem. By integrating CMA with DMA-mapping we managed to
get this driver working with CMA without any single change required in
the driver or videobuf2-dma-contig allocator.

- implement GPF_ATOMIC allocations
- implement support for contiguous memory areas placed in HIGHMEM zone

Best regards
Marek Szyprowski
Samsung Poland R&D Center

Links to previous versions of the patchset:
v11: <>
v10: <>
v9: <>
v8: <>
v7: <>
v6: <>
v5: (intentionally left out as CMA v5 was identical to CMA v4)
v4: <>
v3: <>
v2: <>
v1: <>


1. Fixed 2 nasty bugs in dma-contiguous allocator:
- alignment argument was not passed correctly
- range for dma_release_from_contiguous was not checked correctly

2. Added support for architecture specfic dma_contiguous_early_fixup()

3. CMA and DMA-mapping integration for ARM architechture has been
rewritten to take care of the memory aliasing issue that might
happen for newer ARM CPUs (mapping of the same pages with different
cache attributes is forbidden). TODO: add support for GFP_ATOMIC
allocations basing on the "ARM: DMA: steal memory for DMA coherent
mappings" patch and implement support for contiguous memory areas
that are placed in HIGHMEM zone

1. Removed genalloc usage and replaced it with direct calls to
bitmap_* functions, dropped patches that are not needed
anymore (genalloc extensions)

2. Moved all contiguous area management code from mm/cma.c
to drivers/base/dma-contiguous.c

3. Renamed cm_alloc/free to dma_alloc/release_from_contiguous

4. Introduced global, system wide (default) contiguous area
configured with kernel config and kernel cmdline parameters

5. Simplified initialization to just one function:

6. Added example of device private memory contiguous area

1. Rebased onto 3.0-rc2 and resolved all conflicts

2. Simplified CMA to be just a pure memory allocator, for use
with platfrom/bus specific subsystems, like dma-mapping.
Removed all device specific functions are calls.

3. Integrated with ARM DMA-mapping subsystem.

4. Code cleanup here and there.

5. Removed private context support.

v9: 1. Rebased onto 2.6.39-rc1 and resolved all conflicts

2. Fixed a bunch of nasty bugs that happened when the allocation
failed (mainly kernel oops due to NULL ptr dereference).

3. Introduced testing code: cma-regions compatibility layer and
videobuf2-cma memory allocator module.

v8: 1. The alloc_contig_range() function has now been separated from
CMA and put in page_allocator.c. This function tries to
migrate all LRU pages in specified range and then allocate the
range using alloc_contig_freed_pages().

2. Support for MIGRATE_CMA has been separated from the CMA code.
I have not tested if CMA works with ZONE_MOVABLE but I see no
reasons why it shouldn't.

3. I have added a @private argument when creating CMA contexts so
that one can reserve memory and not share it with the rest of
the system. This way, CMA acts only as allocation algorithm.

v7: 1. A lot of functionality that handled driver->allocator_context
mapping has been removed from the patchset. This is not to say
that this code is not needed, it's just not worth posting
everything in one patchset.

Currently, CMA is "just" an allocator. It uses it's own
migratetype (MIGRATE_CMA) for defining ranges of pageblokcs
which behave just like ZONE_MOVABLE but dispite the latter can
be put in arbitrary places.

2. The migration code that was introduced in the previous version
actually started working.

v6: 1. Most importantly, v6 introduces support for memory migration.
The implementation is not yet complete though.

Migration support means that when CMA is not using memory
reserved for it, page allocator can allocate pages from it.
When CMA wants to use the memory, the pages have to be moved
and/or evicted as to make room for CMA.

To make it possible it must be guaranteed that only movable and
reclaimable pages are allocated in CMA controlled regions.
This is done by introducing a MIGRATE_CMA migrate type that
guarantees exactly that.

Some of the migration code is "borrowed" from Kamezawa
Hiroyuki's alloc_contig_pages() implementation. The main
difference is that thanks to MIGRATE_CMA migrate type CMA
assumes that memory controlled by CMA are is always movable or
reclaimable so that it makes allocation decisions regardless of
the whether some pages are actually allocated and migrates them
if needed.

The most interesting patches from the patchset that implement
the functionality are:

09/13: mm: alloc_contig_free_pages() added
10/13: mm: MIGRATE_CMA migration type added
11/13: mm: MIGRATE_CMA isolation functions added
12/13: mm: cma: Migration support added [wip]

Currently, kernel panics in some situations which I am trying
to investigate.

2. cma_pin() and cma_unpin() functions has been added (after
a conversation with Johan Mossberg). The idea is that whenever
hardware does not use the memory (no transaction is on) the
chunk can be moved around. This would allow defragmentation to
be implemented if desired. No defragmentation algorithm is
provided at this time.

3. Sysfs support has been replaced with debugfs. I always felt
unsure about the sysfs interface and when Greg KH pointed it
out I finally got to rewrite it to debugfs.

v5: (intentionally left out as CMA v5 was identical to CMA v4)

v4: 1. The "asterisk" flag has been removed in favour of requiring
that platform will provide a "*=<regions>" rule in the map

2. The terminology has been changed slightly renaming "kind" to
"type" of memory. In the previous revisions, the documentation
indicated that device drivers define memory kinds and now,

v3: 1. The command line parameters have been removed (and moved to
a separate patch, the fourth one). As a consequence, the
cma_set_defaults() function has been changed -- it no longer
accepts a string with list of regions but an array of regions.

2. The "asterisk" attribute has been removed. Now, each region
has an "asterisk" flag which lets one specify whether this
region should by considered "asterisk" region.

3. SysFS support has been moved to a separate patch (the third one
in the series) and now also includes list of regions.

v2: 1. The "cma_map" command line have been removed. In exchange,
a SysFS entry has been created under kernel/mm/contiguous.

The intended way of specifying the attributes is
a cma_set_defaults() function called by platform initialisation
code. "regions" attribute (the string specified by "cma"
command line parameter) can be overwritten with command line
parameter; the other attributes can be changed during run-time
using the SysFS entries.

2. The behaviour of the "map" attribute has been modified
slightly. Currently, if no rule matches given device it is
assigned regions specified by the "asterisk" attribute. It is
by default built from the region names given in "regions"

3. Devices can register private regions as well as regions that
can be shared but are not reserved using standard CMA
mechanisms. A private region has no name and can be accessed
only by devices that have the pointer to it.

4. The way allocators are registered has changed. Currently,
a cma_allocator_register() function is used for that purpose.
Moreover, allocators are attached to regions the first time
memory is registered from the region or when allocator is
registered which means that allocators can be dynamic modules
that are loaded after the kernel booted (of course, it won't be
possible to allocate a chunk of memory from a region if
allocator is not loaded).

5. Index of new functions:

+static inline dma_addr_t __must_check
+cma_alloc_from(const char *regions, size_t size,
+ dma_addr_t alignment)

+static inline int
+cma_info_about(struct cma_info *info, const const char *regions)

+int __must_check cma_region_register(struct cma_region *reg);

+dma_addr_t __must_check
+cma_alloc_from_region(struct cma_region *reg,
+ size_t size, dma_addr_t alignment);

+static inline dma_addr_t __must_check
+cma_alloc_from(const char *regions,
+ size_t size, dma_addr_t alignment);

+int cma_allocator_register(struct cma_allocator *alloc);

Patches in this patchset:

mm: move some functions from memory_hotplug.c to page_isolation.c
mm: alloc_contig_freed_pages() added

Code "stolen" from Kamezawa. The first patch just moves code
around and the second provide function for "allocates" already
freed memory.

mm: alloc_contig_range() added

This is what Kamezawa asked: a function that tries to migrate all
pages from given range and then use alloc_contig_freed_pages()
(defined by the previous commit) to allocate those pages.

mm: MIGRATE_CMA migration type added
mm: MIGRATE_CMA isolation functions added

Introduction of the new migratetype and support for it in CMA.
MIGRATE_CMA works similar to ZONE_MOVABLE expect almost any
memory range can be marked as one.

mm: cma: Contiguous Memory Allocator added

The code CMA code. Manages CMA contexts and performs memory

ARM: integrate CMA with dma-mapping subsystem

Main client of CMA frame work. CMA serves as a alloc_pages()

ARM: S5PV210: example of CMA private area for FIMC device on Goni board

Example of platform/board specific code that creates cma
context and assigns it to particular device.

Patch summary:

KAMEZAWA Hiroyuki (2):
mm: move some functions from memory_hotplug.c to page_isolation.c
mm: alloc_contig_freed_pages() added

Marek Szyprowski (3):
drivers: add Contiguous Memory Allocator
ARM: integrate CMA with dma-mapping subsystem
ARM: S5PV210: example of CMA private area for FIMC device on Goni

Michal Nazarewicz (3):
mm: alloc_contig_range() added
mm: MIGRATE_CMA migration type added
mm: MIGRATE_CMA isolation functions added

arch/Kconfig | 3 +
arch/arm/Kconfig | 1 +
arch/arm/include/asm/device.h | 3 +
arch/arm/include/asm/dma-contiguous.h | 33 +++
arch/arm/include/asm/mach/map.h | 1 +
arch/arm/mach-s5pv210/Kconfig | 1 +
arch/arm/mach-s5pv210/mach-goni.c | 8 +
arch/arm/mm/dma-mapping.c | 244 +++-----------------
arch/arm/mm/init.c | 3 +
arch/arm/mm/mmu.c | 56 +++++-
drivers/base/Kconfig | 77 +++++++
drivers/base/Makefile | 1 +
drivers/base/dma-contiguous.c | 396 +++++++++++++++++++++++++++++++++
include/linux/dma-contiguous.h | 102 +++++++++
include/linux/mmzone.h | 41 +++-
include/linux/page-isolation.h | 51 ++++-
mm/Kconfig | 8 +-
mm/compaction.c | 10 +
mm/memory_hotplug.c | 111 ---------
mm/page_alloc.c | 287 ++++++++++++++++++++++--
mm/page_isolation.c | 129 ++++++++++-
21 files changed, 1197 insertions(+), 369 deletions(-)
create mode 100644 arch/arm/include/asm/dma-contiguous.h
create mode 100644 drivers/base/dma-contiguous.c
create mode 100644 include/linux/dma-contiguous.h


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