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<h3>
Ben Gamari pushed to branch wip/gc/test
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4>
Commits:
</h4>
<ul>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/a2a9b3ad9fb0807dbdf31da1d6f1ee8196cedabd">a2a9b3ad</a></strong>
<div>
<span>by Ömer Sinan Ağacan</span>
<i>at 2019-06-19T01:40:07Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">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@well-typed.com>
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/fbaf283cc9d30f3e6fc4e5815ce1c9674d41d5d6">fbaf283c</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:40:07Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Add nonmoving WAY
This simply runs the compile_and_run tests with `-xn`, enabling the
nonmoving oldest generation.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/0a07f0e77606fe96cc40de207444572bb5e4f6c6">0a07f0e7</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:40:29Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">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@well-typed.com>
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/f98864faa4e831a1ae5d74c97780ec40a99f6f97">f98864fa</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:40:29Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Nonmoving: Disable memory inventory with concurrent collection
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/b44c267feedbfd681fd2bce319068b528a5a3900">b44c267f</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:49Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Add nonmoving_thr way
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/37cf91733720a3fb077b62a832d882239579a21e">37cf9173</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:49Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Add nonmoving_thr_ghc way
This uses the nonmoving collector when compiling the testcases.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/1ac956e0eed1f13c16be5db3742bc65f9bc83249">1ac956e0</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Don't run T15892 in nonmoving ways
The nonmoving GC doesn't support `+RTS -G1`, which this test insists on.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/d51f62abd8686b5bb438f899ed180f8d2372eb33">d51f62ab</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Nonmoving collector doesn't support -G1
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/b14784df7cd384c9775efae26691c48305d31ab2">b14784df</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Ensure that threaded tests are run in nonmoving_thr
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/1a286242aeddffba411a891741480a8969658fe6">1a286242</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: bug1010 requires -c, which isn't supported by nonmoving
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/eedd46ddb2998c5f084e4e98868da959e42f68e8">eedd46dd</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">testsuite: Skip T15892 in nonmoving_thr_ghc
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/8b65a9cd40034ae1167c50eecfff9e1150d8a117">8b65a9cd</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">ghc-heap: Skip heap_all test with debugged RTS
The debugged RTS initializes the heap with 0xaa, which breaks the
(admittedly rather fragile) assumption that uninitialized fields are set
to 0x00:
```
Wrong exit code for heap_all(nonmoving)(expected 0 , actual 1 )
Stderr ( heap_all ):
heap_all: user error (assertClosuresEq: Closures do not match
Expected: FunClosure {info = StgInfoTable {entry = Nothing, ptrs = 0, nptrs = 1, tipe = FUN_0_1, srtlen = 0, code = Nothing}, ptrArgs = [], dataArgs = [0]}
Actual: FunClosure {info = StgInfoTable {entry = Nothing, ptrs = 0, nptrs = 1, tipe = FUN_0_1, srtlen = 1032832, code = Nothing}, ptrArgs = [], dataArgs = [12297829382473034410]}
CallStack (from HasCallStack):
assertClosuresEq, called at heap_all.hs:230:9 in main:Main
)
```
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/commit/da9e3ef2f0eb9943159444953d14d2fd4b6bff5e">da9e3ef2</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2019-06-19T01:41:50Z</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Skip ghc_heap_all test in nonmoving ways
</pre>
</li>
</ul>
<h4>30 changed files:</h4>
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<a href="#db6936871693fa68c3fdcbd692eb7dcffc3a9372">
compiler/cmm/CLabel.hs
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<a href="#c10b1b0056f54b8b89286ac4a327928f83cf8ab6">
compiler/codeGen/StgCmmBind.hs
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<a href="#731b07c16b2f4bb31dd7defa4ceef54e74473cc7">
compiler/codeGen/StgCmmPrim.hs
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<a href="#5f05b3e433aad7b0e6e5aa2aae206d359bb54f4c">
compiler/codeGen/StgCmmUtils.hs
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<a href="#6011cad13b19136953f8ee72df01a66623c5c1b0">
includes/Cmm.h
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includes/Rts.h
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includes/rts/NonMoving.h
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includes/rts/storage/Block.h
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includes/rts/storage/ClosureMacros.h
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<a href="#94ca41c5afbb3d932bd6f37ee16458322988fb69">
includes/rts/storage/GC.h
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<a href="#2f870b7c76a5e24010e464cc1a1f860c0f9e0dab">
includes/rts/storage/TSO.h
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<a href="#89ed911ca15ec0db941eb82e8d7df8453f4ab713">
includes/stg/MiscClosures.h
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<a href="#e7e177c17e4bf37dc865a39cde7a0ec9e1a33362">
libraries/ghc-heap/tests/all.T
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rts/Apply.cmm
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rts/Capability.c
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rts/Capability.h
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rts/Exception.cmm
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rts/Messages.c
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rts/PrimOps.cmm
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rts/RaiseAsync.c
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rts/RtsStartup.c
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rts/RtsSymbols.c
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rts/STM.c
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rts/Schedule.c
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rts/StableName.c
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rts/ThreadPaused.c
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rts/Threads.c
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rts/Updates.h
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<a href="#8a78f03f80f0544ead476d53dd0f1db7cbd68d1b">
rts/Weak.c
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<a href="#37a93df244a7789fddf557443b6398d06763e9cc">
rts/sm/Evac.c
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<h5>The diff was not included because it is too large.</h5>
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