Commits on Source (55)
-
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.
-
Ben Gamari authored -
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
-
-
-
-
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.
-
Ben Gamari authored
-
These will be needed when we implement sweeping in the nonmoving collector.
-
This warning is a bit of a relic; there is little reason to avoid aggregate return values in 2019.
-
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.
-
This flag will enable the use of a non-moving oldest generation.
-
-
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>
-
This simply runs the compile_and_run tests with `-xn`, enabling the nonmoving oldest generation.
-
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>
-
Ben Gamari authored
-
This introduces a few events to mark key points in the nonmoving garbage collection cycle. These include: * `EVENT_CONC_MARK_BEGIN`, denoting the beginning of a round of marking. This may happen more than once in a single major collection since we the major collector iterates until it hits a fixed point. * `EVENT_CONC_MARK_END`, denoting the end of a round of marking. * `EVENT_CONC_SYNC_BEGIN`, denoting the beginning of the post-mark synchronization phase * `EVENT_CONC_UPD_REM_SET_FLUSH`, indicating that a capability has flushed its update remembered set. * `EVENT_CONC_SYNC_END`, denoting that all mutators have flushed their update remembered sets. * `EVENT_CONC_SWEEP_BEGIN`, denoting the beginning of the sweep portion of the major collection. * `EVENT_CONC_SWEEP_END`, denoting the end of the sweep portion of the major collection.
-
This introduces a simple census of the non-moving heap (not to be confused with the heap census used by the heap profiler). This collects basic heap usage information (number of allocated and free blocks) which is useful when characterising fragmentation of the nonmoving heap.
-
Ben Gamari authored
-
Ben Gamari authored
Otherwise the census is unsafe when mutators are running due to concurrent mutation.
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
This commit does two things: * Allow aging of objects during the preparatory minor GC * Refactor handling of static objects to avoid the use of a hashtable
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
This uses the nonmoving collector when compiling the testcases.
-
Ben Gamari authored
The nonmoving GC doesn't support `+RTS -G1`, which this test insists on.
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
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 ) ``` -
Ben Gamari authored
-
Ben Gamari authored
Perf showed that the this single div was capturing up to 10% of samples in nonmovingMark. However, the overwhelming majority of cases is looking at small block sizes. These cases we can easily compute explicitly, allowing the compiler to turn the division into a significantly more efficient division-by-constant. While the increase in source code looks scary, this all optimises down to very nice looking assembler. At this point the only remaining hotspots in nonmovingBlockCount are due to memory access.
-
Ben Gamari authored
-
Ben Gamari authored
This shortens MarkQueueEntry by 30% (one word)
-
Ben Gamari authored
Use memchr instead of a open-coded loop. This is nearly twice as fast in a synthetic benchmark.
-
Ben Gamari authored
-
Ben Gamari authored
Ensure that the bitmap of the segmentt that we will clear next is in cache by the time we reach it.
-
Ben Gamari authored
-
Ben Gamari authored
-
Ben Gamari authored
This improved overall runtime on nofib's constraints test by nearly 10%.
-
Ben Gamari authored
-
Ben Gamari authored
Previously we would look at the segment header to determine the block size despite the fact that we already had the block size at hand.
-
Ben Gamari authored
-
Ben Gamari authored
Previously we would perform a preparatory moving collection, resulting in many things being added to the mark queue. When we finished with this we would realize in nonmovingCollect that there was already a collection running, in which case we would simply not run the nonmoving collector. However, it was very easy to end up in a "treadmilling" situation: all subsequent GC following the first failed major GC would be scheduled as major GCs. Consequently we would continuously feed the concurrent collector with more mark queue entries and it would never finish. This patch aborts the major collection far earlier, meaning that we avoid adding nonmoving objects to the mark queue and allowing the concurrent collector to finish.
-
Ben Gamari authored
-
Ben Gamari authored
-
This allows indirection chains residing in the non-moving heap to be shorted-out.
-
includes/rts/NonMoving.h
0 → 100644