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authorBen Gamari <ben@smart-cactus.org>2020-03-03 23:42:14 -0500
committerMarge Bot <ben+marge-bot@smart-cactus.org>2020-03-14 05:28:43 -0400
commit20d4d676964382b313b9e44062e45a7c38621999 (patch)
treed575a7cf7de04ad22bb309ac22baef311464a907
parent7c3e39a9a7ccb3b6c2953b0397a0d315dc0ec7d5 (diff)
downloadhaskell-20d4d676964382b313b9e44062e45a7c38621999.tar.gz
nonmoving: Don't traverse filled segment list in pause
The non-moving collector would previously walk the entire filled segment list during the preparatory pause. However, this is far more work than is strictly necessary. We can rather get away with merely collecting the allocators' filled segment list heads and process the lists themselves during the concurrent phase. This can significantly reduce the maximum gen1 GC pause time in programs with high rates of long-lived allocations.
-rw-r--r--rts/sm/NonMoving.c43
-rw-r--r--rts/sm/NonMoving.h1
2 files changed, 26 insertions, 18 deletions
diff --git a/rts/sm/NonMoving.c b/rts/sm/NonMoving.c
index fe9d22b479..bdf22dc37b 100644
--- a/rts/sm/NonMoving.c
+++ b/rts/sm/NonMoving.c
@@ -727,25 +727,10 @@ static void nonmovingPrepareMark(void)
nonmovingSegmentInfo(seg)->next_free_snap = seg->next_free;
}
- // Update filled segments' snapshot pointers and move to sweep_list
- uint32_t n_filled = 0;
- struct NonmovingSegment *const filled = alloca->filled;
+ // Save the filled segments for later processing during the concurrent
+ // mark phase.
+ alloca->saved_filled = alloca->filled;
alloca->filled = NULL;
- if (filled) {
- struct NonmovingSegment *seg = filled;
- while (true) {
- // Set snapshot
- nonmovingSegmentInfo(seg)->next_free_snap = seg->next_free;
- n_filled++;
- if (seg->link)
- seg = seg->link;
- else
- break;
- }
- // add filled segments to sweep_list
- seg->link = nonmovingHeap.sweep_list;
- nonmovingHeap.sweep_list = filled;
- }
// N.B. It's not necessary to update snapshot pointers of active segments;
// they were set after they were swept and haven't seen any allocation
@@ -969,6 +954,28 @@ static void nonmovingMark_(MarkQueue *mark_queue, StgWeak **dead_weaks, StgTSO *
debugTrace(DEBUG_nonmoving_gc, "Starting mark...");
stat_startNonmovingGc();
+ // Walk the list of filled segments that we collected during preparation,
+ // updated their snapshot pointers and move them to the sweep list.
+ for (int alloca_idx = 0; alloca_idx < NONMOVING_ALLOCA_CNT; ++alloca_idx) {
+ struct NonmovingSegment *filled = nonmovingHeap.allocators[alloca_idx]->saved_filled;
+ uint32_t n_filled = 0;
+ if (filled) {
+ struct NonmovingSegment *seg = filled;
+ while (true) {
+ // Set snapshot
+ nonmovingSegmentInfo(seg)->next_free_snap = seg->next_free;
+ n_filled++;
+ if (seg->link)
+ seg = seg->link;
+ else
+ break;
+ }
+ // add filled segments to sweep_list
+ seg->link = nonmovingHeap.sweep_list;
+ nonmovingHeap.sweep_list = filled;
+ }
+ }
+
// Do concurrent marking; most of the heap will get marked here.
nonmovingMarkThreadsWeaks(mark_queue);
diff --git a/rts/sm/NonMoving.h b/rts/sm/NonMoving.h
index 36ecd8b0af..6eabcb8493 100644
--- a/rts/sm/NonMoving.h
+++ b/rts/sm/NonMoving.h
@@ -62,6 +62,7 @@ struct NonmovingSegment {
// A non-moving allocator for a particular block size
struct NonmovingAllocator {
struct NonmovingSegment *filled;
+ struct NonmovingSegment *saved_filled;
struct NonmovingSegment *active;
// indexed by capability number
struct NonmovingSegment *current[];