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Subject[PATCHv8 00/12] Contiguous Memory Allocator
Hello everyone,

This is yet another version of CMA this time stripped from a lot of
code and with working migration implementation.

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

For more information see 7th patch in the set.


This version fixes some things Kamezawa suggested plus it separates
code that uses MIGRATE_CMA from the rest of the code. This I hope
will help to grasp the overall idea of CMA.


The current version is just an allocator that handles allocation of
contiguous memory blocks. The difference between this patchset and
Kamezawa's alloc_contig_pages() are:

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

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 cm_alloc()/cm_free()
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.


Links to previous versions of the patchset:
v7: <http://article.gmane.org/gmane.linux.kernel.mm/55626>
v6: <http://article.gmane.org/gmane.linux.kernel.mm/55626>
v5: (intentionally left out as CMA v5 was identical to CMA v4)
v4: <http://article.gmane.org/gmane.linux.kernel.mm/52010>
v3: <http://article.gmane.org/gmane.linux.kernel.mm/51573>
v2: <http://article.gmane.org/gmane.linux.kernel.mm/50986>
v1: <http://article.gmane.org/gmane.linux.kernel.mm/50669>


Changelog:

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
attribute.

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"
attribute.

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: migrate.c: fix compilation error

I had some strange compilation error; this patch fixed them.

lib: bitmap: Added alignment offset for bitmap_find_next_zero_area()
lib: genalloc: Generic allocator improvements

Some improvements to genalloc API (most importantly possibility to
allocate memory with alignment requirement).

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: cma: Contiguous Memory Allocator added

The CMA code but with no MIGRATE_CMA support yet. This assues
that one uses a ZONE_MOVABLE. I must admit I have not test that
setup yet but I don't see any reasons why it should not work.

mm: MIGRATE_CMA migration type added
mm: MIGRATE_CMA isolation functions added
mm: MIGRATE_CMA support added to CMA

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: Test device and application added

Test device and application. Not really for merging; just for
testing really.

ARM: cma: Added CMA to Aquila, Goni and c210 universal boards

A stub integration with some ARM machines. Mostly to get the cma
testing device working. Again, not for merging, just an example.


arch/arm/mach-s5pv210/Kconfig | 2 +
arch/arm/mach-s5pv210/mach-aquila.c | 2 +
arch/arm/mach-s5pv210/mach-goni.c | 2 +
arch/arm/mach-s5pv310/Kconfig | 1 +
arch/arm/mach-s5pv310/mach-universal_c210.c | 2 +
arch/arm/plat-s5p/Makefile | 2 +
arch/arm/plat-s5p/cma-stub.c | 49 +++
arch/arm/plat-s5p/include/plat/cma-stub.h | 21 ++
drivers/misc/Kconfig | 28 ++
drivers/misc/Makefile | 1 +
drivers/misc/cma-dev.c | 238 ++++++++++++++
include/linux/bitmap.h | 24 ++-
include/linux/cma.h | 290 +++++++++++++++++
include/linux/genalloc.h | 46 ++--
include/linux/mmzone.h | 43 ++-
include/linux/page-isolation.h | 50 +++-
lib/bitmap.c | 22 +-
lib/genalloc.c | 182 ++++++-----
mm/Kconfig | 36 ++
mm/Makefile | 1 +
mm/cma.c | 455 ++++++++++++++++++++++++++
mm/compaction.c | 10 +
mm/internal.h | 3 +
mm/memory_hotplug.c | 108 -------
mm/migrate.c | 2 +
mm/page_alloc.c | 286 +++++++++++++++--
mm/page_isolation.c | 126 +++++++-
tools/cma/cma-test.c | 457 +++++++++++++++++++++++++++
28 files changed, 2219 insertions(+), 270 deletions(-)
create mode 100644 arch/arm/plat-s5p/cma-stub.c
create mode 100644 arch/arm/plat-s5p/include/plat/cma-stub.h
create mode 100644 drivers/misc/cma-dev.c
create mode 100644 include/linux/cma.h
create mode 100644 mm/cma.c
create mode 100644 tools/cma/cma-test.c
--
1.7.2.3



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