[Git][ghc/ghc][wip/gc/nonmoving-concurrent] 19 commits: rts/BlockAlloc: Allow aligned allocation requests
Ben Gamari
gitlab at gitlab.haskell.org
Wed Jun 19 00:40:03 UTC 2019
Ben Gamari pushed to branch wip/gc/nonmoving-concurrent at Glasgow Haskell Compiler / GHC
Commits:
80a5d3e1 by Ömer Sinan Ağacan at 2019-06-19T00:30:19Z
rts/BlockAlloc: Allow aligned allocation requests
This implements support for block group allocations which are aligned to
an integral number of blocks.
This will be used by the nonmoving garbage collector, which uses the
block allocator to allocate the segments which back its heap. These
segments are a fixed number of blocks in size, with each segment being
aligned to the segment size boundary. This allows us to easily find the
segment metadata stored at the beginning of the segment.
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530e6824 by Ben Gamari at 2019-06-19T00:30:19Z
testsuite/testblockalloc: A bit of refactoring
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7c0652b3 by Ben Gamari at 2019-06-19T00:30:19Z
testsuite/testblockalloc: Test aligned block group allocation
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ac705426 by Ben Gamari at 2019-06-19T00:30:20Z
rts/BlockAlloc: Wibbles
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8788c063 by Ben Gamari at 2019-06-19T00:30:20Z
rts/BlockAlloc: Use allocLargeChunk in aligned block allocation
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f3191083 by Ömer Sinan Ağacan at 2019-06-19T00:32:01Z
Disallow allocating megablocks, update tests
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67cbec4a by Ömer Sinan Ağacan at 2019-06-19T00:32:01Z
Fix lint errors
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59d32a99 by Ömer Sinan Ağacan at 2019-06-19T00:32:01Z
Use allocLargeChunkOnNode to reduce splitting
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ead67e40 by Ömer Sinan Ağacan at 2019-06-19T00:32:01Z
Allow allocating megablocks in allocAlignedGroupOnNode
This is currently broken because freeGroup assumes integral number of
megablocks when freeing megablocks but we try to split the megablocks
returned by allocLargeChunkOnNode to smaller groups and free the rest.
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5fab1847 by Ben Gamari at 2019-06-19T00:32:46Z
Merge branches 'wip/gc/misc-rts' and 'wip/gc/aligned-block-allocation' into wip/gc/preparation
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7cb5b05c by Ömer Sinan Ağacan at 2019-06-19T00:33:55Z
rts/StableName: Expose FOR_EACH_STABLE_NAME, freeSnEntry, SNT_size
These will be needed when we implement sweeping in the nonmoving
collector.
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98c601f2 by Ben Gamari at 2019-06-19T00:33:55Z
rts: Disable aggregate-return warnings from gcc
This warning is a bit of a relic; there is little reason to avoid
aggregate return values in 2019.
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225afe49 by Ömer Sinan Ağacan at 2019-06-19T00:33:55Z
rts/Scav: Expose scavenging functions
To keep the non-moving collector nicely separated from the moving
collector its scavenging phase will live in another file,
`NonMovingScav.c`. However, it will need to use these functions so
let's expose them.
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babf1fb8 by Ben Gamari at 2019-06-19T00:33:55Z
rts: Introduce flag to enable the nonmoving old generation
This flag will enable the use of a non-moving oldest generation.
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f1639975 by Ben Gamari at 2019-06-19T00:33:55Z
rts: Introduce debug flag for non-moving GC
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85a47315 by Ömer Sinan Ağacan at 2019-06-19T00:33:55Z
rts: Non-concurrent mark and sweep
This implements the core heap structure and a serial mark/sweep
collector which can be used to manage the oldest-generation heap.
This is the first step towards a concurrent mark-and-sweep collector
aimed at low-latency applications.
The full design of the collector implemented here is described in detail
in a technical note
B. Gamari. "A Concurrent Garbage Collector For the Glasgow Haskell
Compiler" (2018)
The basic heap structure used in this design is heavily inspired by
K. Ueno & A. Ohori. "A fully concurrent garbage collector for
functional programs on multicore processors." /ACM SIGPLAN Notices/
Vol. 51. No. 9 (presented by ICFP 2016)
This design is intended to allow both marking and sweeping
concurrent to execution of a multi-core mutator. Unlike the Ueno design,
which requires no global synchronization pauses, the collector
introduced here requires a stop-the-world pause at the beginning and end
of the mark phase.
To avoid heap fragmentation, the allocator consists of a number of
fixed-size /sub-allocators/. Each of these sub-allocators allocators into
its own set of /segments/, themselves allocated from the block
allocator. Each segment is broken into a set of fixed-size allocation
blocks (which back allocations) in addition to a bitmap (used to track
the liveness of blocks) and some additional metadata (used also used
to track liveness).
This heap structure enables collection via mark-and-sweep, which can be
performed concurrently via a snapshot-at-the-beginning scheme (although
concurrent collection is not implemented in this patch).
The mark queue is a fairly straightforward chunked-array structure.
The representation is a bit more verbose than a typical mark queue to
accomodate a combination of two features:
* a mark FIFO, which improves the locality of marking, reducing one of
the major overheads seen in mark/sweep allocators (see [1] for
details)
* the selector optimization and indirection shortcutting, which
requires that we track where we found each reference to an object
in case we need to update the reference at a later point (e.g. when
we find that it is an indirection). See Note [Origin references in
the nonmoving collector] (in `NonMovingMark.h`) for details.
Beyond this the mark/sweep is fairly run-of-the-mill.
[1] R. Garner, S.M. Blackburn, D. Frampton. "Effective Prefetch for
Mark-Sweep Garbage Collection." ISMM 2007.
Co-Authored-By: Ben Gamari <ben at well-typed.com>
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044531d5 by Ben Gamari at 2019-06-19T00:33:55Z
testsuite: Add nonmoving WAY
This simply runs the compile_and_run tests with `-xn`, enabling the
nonmoving oldest generation.
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d468f6f1 by Ben Gamari at 2019-06-19T00:34:36Z
rts: Implement concurrent collection in the nonmoving collector
This extends the non-moving collector to allow concurrent collection.
The full design of the collector implemented here is described in detail
in a technical note
B. Gamari. "A Concurrent Garbage Collector For the Glasgow Haskell
Compiler" (2018)
This extension involves the introduction of a capability-local
remembered set, known as the /update remembered set/, which tracks
objects which may no longer be visible to the collector due to mutation.
To maintain this remembered set we introduce a write barrier on
mutations which is enabled while a concurrent mark is underway.
The update remembered set representation is similar to that of the
nonmoving mark queue, being a chunked array of `MarkEntry`s. Each
`Capability` maintains a single accumulator chunk, which it flushed
when it (a) is filled, or (b) when the nonmoving collector enters its
post-mark synchronization phase.
While the write barrier touches a significant amount of code it is
conceptually straightforward: the mutator must ensure that the referee
of any pointer it overwrites is added to the update remembered set.
However, there are a few details:
* In the case of objects with a dirty flag (e.g. `MVar`s) we can
exploit the fact that only the *first* mutation requires a write
barrier.
* Weak references, as usual, complicate things. In particular, we must
ensure that the referee of a weak object is marked if dereferenced by
the mutator. For this we (unfortunately) must introduce a read
barrier, as described in Note [Concurrent read barrier on deRefWeak#]
(in `NonMovingMark.c`).
* Stable names are also a bit tricky as described in Note [Sweeping
stable names in the concurrent collector] (`NonMovingSweep.c`).
We take quite some pains to ensure that the high thread count often seen
in parallel Haskell applications doesn't affect pause times. To this end
we allow thread stacks to be marked either by the thread itself (when it
is executed or stack-underflows) or the concurrent mark thread (if the
thread owning the stack is never scheduled). There is a non-trivial
handshake to ensure that this happens without racing which is described
in Note [StgStack dirtiness flags and concurrent marking].
Co-Authored-by: Ömer Sinan Ağacan <omer at well-typed.com>
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364e2b37 by Ben Gamari at 2019-06-19T00:34:36Z
Nonmoving: Disable memory inventory with concurrent collection
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30 changed files:
- compiler/cmm/CLabel.hs
- compiler/codeGen/StgCmmBind.hs
- compiler/codeGen/StgCmmPrim.hs
- compiler/codeGen/StgCmmUtils.hs
- docs/users_guide/runtime_control.rst
- includes/Cmm.h
- includes/Rts.h
- includes/rts/Flags.h
- + includes/rts/NonMoving.h
- includes/rts/storage/Block.h
- includes/rts/storage/ClosureMacros.h
- includes/rts/storage/GC.h
- includes/rts/storage/TSO.h
- includes/stg/MiscClosures.h
- libraries/base/GHC/RTS/Flags.hsc
- rts/Apply.cmm
- rts/Capability.c
- rts/Capability.h
- rts/Exception.cmm
- rts/Messages.c
- rts/PrimOps.cmm
- rts/RaiseAsync.c
- rts/RtsFlags.c
- rts/RtsStartup.c
- rts/RtsSymbols.c
- rts/STM.c
- rts/Schedule.c
- rts/Schedule.h
- rts/StableName.c
- rts/StableName.h
The diff was not included because it is too large.
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/compare/c531a2567d3dde9c9ed5e20deae002520c2f4702...364e2b3768e3fc86eec99c72f4272a54a5f44958
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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/compare/c531a2567d3dde9c9ed5e20deae002520c2f4702...364e2b3768e3fc86eec99c72f4272a54a5f44958
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