[PATCHv20 00/15] Contiguous Memory Allocator

From: Marek Szyprowski
Date: Fri Feb 03 2012 - 07:23:37 EST

Welcome everyone again!

This is yet another quick update on Contiguous Memory Allocator patches.
This version includes another set of code cleanups requested by Mel
Gorman and a few minor bug fixes. I really hope that this version will
be accepted for merging and future development will be handled by
incremental patches.

ARM integration code has not been changed since v16. It provides
implementation of the ideas that has been discussed during Linaro Sprint
meeting in Cambourne, August 2011. Here are the details:

This version provides a solution for complete integration of CMA to
DMA mapping subsystem on ARM architecture. The issue caused by double
dma pages mapping and possible aliasing in coherent memory mapping has
been finally resolved, both for GFP_ATOMIC case (allocations comes from
coherent memory pool) and non-GFP_ATOMIC case (allocations comes from
CMA managed areas).

For coherent, nommu, ARMv4 and ARMv5 systems the current DMA-mapping
implementation has been kept.

For ARMv6+ systems, CMA has been enabled and a special pool of coherent
memory for atomic allocations has been created. The size of this pool
defaults to DEFAULT_CONSISTEN_DMA_SIZE/8, but can be changed with
coherent_pool kernel parameter (if really required).

All atomic allocations are served from this pool. I've did a little
simplification here, because there is no separate pool for writecombine
memory - such requests are also served from coherent pool. I don't
think that such simplification is a problem here - I found no driver
that use dma_alloc_writecombine with GFP_ATOMIC flags.

All non-atomic allocation are served from CMA area. Kernel mappings are
updated to reflect required memory attributes changes. This is possible
because during early boot, all CMA area are remapped with 4KiB pages in
kernel low-memory.

This version have been tested on Samsung S5PC110 based Goni machine and
Exynos4 UniversalC210 board with various V4L2 multimedia drivers.

Coherent atomic allocations has been tested by manually enabling the dma
bounce for the s3c-sdhci device.

All patches are prepared on top of Linux Kernel v3.3-rc2.

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:
http://lwn.net/Articles/447405/ and http://lwn.net/Articles/450286/
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. Since version v17
Michal is working again on CMA patches and the current version is
the result of our joint open-source effort.

Best regards
Marek Szyprowski
Samsung Poland R&D Center

Links to previous versions of the patchset:
v19: <http://www.spinics.net/lists/linux-mm/msg29145.html>
v18: <http://www.spinics.net/lists/linux-mm/msg28125.html>
v17: <http://www.spinics.net/lists/arm-kernel/msg148499.html>
v16: <http://www.spinics.net/lists/linux-mm/msg25066.html>
v15: <http://www.spinics.net/lists/linux-mm/msg23365.html>
v14: <http://www.spinics.net/lists/linux-media/msg36536.html>
v13: (internal, intentionally not released)
v12: <http://www.spinics.net/lists/linux-media/msg35674.html>
v11: <http://www.spinics.net/lists/linux-mm/msg21868.html>
v10: <http://www.spinics.net/lists/linux-mm/msg20761.html>
v9: <http://article.gmane.org/gmane.linux.kernel.mm/60787>
v8: <http://article.gmane.org/gmane.linux.kernel.mm/56855>
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>


1. Addressed even more comments from Mel Gorman and added his Acked-by tag
on most of the core memory management patches.

2. Squashed a few minor fixes here and there (corrected alignment calculation
for region limit, added adjusting low watermark level on reclaim, fixed
return value of __alloc_contig_migrate_range function)

3. Removed problematic "mm: page_alloc: update migrate type of pages on pcp
when isolating" patch and sligtly altered MIGRATE_CMA type handling what
solved the problem

4. Rebased onto v3.3-rc2

1. Addressed another set of comments and suggestions from Mel Gorman, mainly
related to breaking patches into smaller, single-feature related chunks
and rewriting already existing functions in memory compaction code.

2. Reworked completely page reclaim code, removed it from split_free_page()
and introduce direct call from alloc_contig_range().

3. Merged a fix from Mans Rullgard for correct cma area limit alignment.

4. Replaced broken "mm: page_alloc: set_migratetype_isolate: drain PCP prior
to isolating" patch with "mm: page_alloc: update migrate type of pages on
pcp when isolating" which is another attempt to solve this issue without
touching free_pcppages_bulk().

5. Rebased onto v3.3-rc1

1. Addressed comments and suggestions from Mel Gorman related to changes
in memory compaction code, most important points:
- removed "mm: page_alloc: handle MIGRATE_ISOLATE in free_pcppages_bulk()"
and moved all the logic to set_migratetype_isolate - see
"mm: page_alloc: set_migratetype_isolate: drain PCP prior to isolating"
- code in "mm: compaction: introduce isolate_{free,migrate}pages_range()"
patch have been simplified and improved
- removed "mm: mmzone: introduce zone_pfn_same_memmap()" patch

2. Fixed crash on initialization if HIGHMEM is available on ARM platforms

3. Fixed problems with allocation of contiguous memory if all free pages
are occupied by page cache and reclaim is required.

4. Added a workaround for temporary migration failures (now CMA tries
to allocate different memory block in such case), what heavily increased
reliability of the CMA.

5. Minor cleanup here and there.

6. Rebased onto v3.2-rc7 kernel tree.

1. Replaced whole CMA core memory migration code to the new one kindly
provided by Michal Nazarewicz. The new code is based on memory
compaction framework not the memory hotplug, like it was before. This
change has been suggested by Mel Godman.

2. Addressed most of the comments from Andrew Morton and Mel Gorman in
the rest of the CMA code.

3. Fixed broken initialization on ARM systems with DMA zone enabled.

4. Rebased onto v3.2-rc2 kernel.

1. merged a fixup from Michal Nazarewicz to address comments from Dave
Hansen about checking if pfns belong to the same memory zone

2. merged a fix from Michal Nazarewicz for incorrect handling of pages
which belong to page block that is in MIGRATE_ISOLATE state, in very
rare cases the migrate type of page block might have been changed
from MIGRATE_CMA to MIGRATE_MOVABLE because of this bug

3. moved some common code to include/asm-generic

4. added support for x86 DMA-mapping framework for pci-dma hardware,
CMA can be now even more widely tested on KVM/QEMU and a lot of common
x86 boxes

5. rebased onto next-20111005 kernel tree, which includes changes in ARM
DMA-mapping subsystem (CONSISTENT_DMA_SIZE removal)

6. removed patch for CMA s5p-fimc device private regions (served only as
example) and provided the one that matches real life case - s5p-mfc

1. fixed calculation of the total memory after activating CMA area (was
broken from v12)

2. more code cleanup in drivers/base/dma-contiguous.c

3. added address limit for default CMA area

4. rewrote ARM DMA integration:
- removed "ARM: DMA: steal memory for DMA coherent mappings" patch
- kept current DMA mapping implementation for coherent, nommu and
ARMv4/ARMv5 systems
- enabled CMA for all ARMv6+ systems
- added separate, small pool for coherent atomic allocations, defaults
to CONSISTENT_DMA_SIZE/8, but can be changed with kernel parameter

1. Merged with "ARM: DMA: steal memory for DMA coherent mappings"
patch, added support for GFP_ATOMIC allocations.

2. Added checks for NULL device pointer

v13: (internal, intentionally not released)

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:

Marek Szyprowski (6):
mm: extract reclaim code from __alloc_pages_direct_reclaim()
mm: trigger page reclaim in alloc_contig_range() to stabilize
drivers: add Contiguous Memory Allocator
X86: integrate CMA with DMA-mapping subsystem
ARM: integrate CMA with DMA-mapping subsystem
ARM: Samsung: use CMA for 2 memory banks for s5p-mfc device

Michal Nazarewicz (9):
mm: page_alloc: remove trailing whitespace
mm: compaction: introduce isolate_migratepages_range().
mm: compaction: introduce map_pages()
mm: compaction: introduce isolate_freepages_range()
mm: compaction: export some of the functions
mm: page_alloc: introduce alloc_contig_range()
mm: page_alloc: change fallbacks array handling
mm: mmzone: MIGRATE_CMA migration type added
mm: page_isolation: MIGRATE_CMA isolation functions added

Documentation/kernel-parameters.txt | 9 +
arch/Kconfig | 3 +
arch/arm/Kconfig | 2 +
arch/arm/include/asm/dma-contiguous.h | 16 ++
arch/arm/include/asm/mach/map.h | 1 +
arch/arm/kernel/setup.c | 9 +-
arch/arm/mm/dma-mapping.c | 368 ++++++++++++++++++++++++------
arch/arm/mm/init.c | 22 ++-
arch/arm/mm/mm.h | 3 +
arch/arm/mm/mmu.c | 31 ++-
arch/arm/plat-s5p/dev-mfc.c | 51 +----
arch/x86/Kconfig | 1 +
arch/x86/include/asm/dma-contiguous.h | 13 +
arch/x86/include/asm/dma-mapping.h | 4 +
arch/x86/kernel/pci-dma.c | 18 ++-
arch/x86/kernel/pci-nommu.c | 8 +-
arch/x86/kernel/setup.c | 2 +
drivers/base/Kconfig | 89 +++++++
drivers/base/Makefile | 1 +
drivers/base/dma-contiguous.c | 405 ++++++++++++++++++++++++++++++++
include/asm-generic/dma-contiguous.h | 27 ++
include/linux/device.h | 4 +
include/linux/dma-contiguous.h | 110 +++++++++
include/linux/gfp.h | 12 +
include/linux/mmzone.h | 38 +++-
include/linux/page-isolation.h | 18 +-
mm/Kconfig | 2 +-
mm/Makefile | 3 +-
mm/compaction.c | 418 +++++++++++++++++++++------------
mm/internal.h | 33 +++
mm/memory-failure.c | 2 +-
mm/memory_hotplug.c | 6 +-
mm/page_alloc.c | 377 ++++++++++++++++++++++++++---
mm/page_isolation.c | 15 +-
mm/vmstat.c | 3 +
35 files changed, 1757 insertions(+), 367 deletions(-)
create mode 100644 arch/arm/include/asm/dma-contiguous.h
create mode 100644 arch/x86/include/asm/dma-contiguous.h
create mode 100644 drivers/base/dma-contiguous.c
create mode 100644 include/asm-generic/dma-contiguous.h
create mode 100644 include/linux/dma-contiguous.h


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