diff options
| -rw-r--r-- | rts/sm/GCUtils.c | 48 | ||||
| -rw-r--r-- | testsuite/tests/rts/all.T | 1 |
2 files changed, 35 insertions, 14 deletions
diff --git a/rts/sm/GCUtils.c b/rts/sm/GCUtils.c index 84a620e8e7..1c6a93c3b2 100644 --- a/rts/sm/GCUtils.c +++ b/rts/sm/GCUtils.c @@ -138,9 +138,11 @@ push_scanned_block (bdescr *bd, gen_workspace *ws) ASSERT(bd->gen == ws->gen); ASSERT(bd->u.scan == bd->free); - if (bd->start + bd->blocks * BLOCK_SIZE_W - bd->free > WORK_UNIT_WORDS) + if (bd->blocks == 1 && + bd->start + BLOCK_SIZE_W - bd->free > WORK_UNIT_WORDS) { - // a partially full block: put it on the part_list list. + // A partially full block: put it on the part_list list. + // Only for single objects - see Note [big objects] bd->link = ws->part_list; ws->part_list = bd; ws->n_part_blocks += bd->blocks; @@ -158,6 +160,35 @@ push_scanned_block (bdescr *bd, gen_workspace *ws) } } +/* Note [big objects] + + We can get an ordinary object (CONSTR, FUN, THUNK etc.) that is + larger than a block (see #7919). Let's call these "big objects". + These objects don't behave like large objects - they live in + ordinary heap space (not the large_objects list), and are copied by + evacuate(). + + Clearly to copy one of these objects we need a block group, not an + ordinary block, so when alloc_todo_block() will correctly allocate a + block group. + + The question is what to do with the space that is left at the end + of the block group after copying the big object into it. We could + continue to copy more objects into that space, but unfortunately + the rest of the GC is not set up to handle objects that start in + the second or later blocks of a group. We just about manage this + in the nursery (see scheduleHandleHeapOverflow()) so evacuate() can + handle this, but other parts of the GC can't. We could probably + fix this, but it's a rare case, so for now we ensure that we never + copy objects into the second and subsequent blocks of a block + group. + + To ensure this: + - alloc_todo_block() sets todo_lim to be exactly the size of the + large object + - push_scanned_block doesn't put these blocks on the part_list +*/ + StgPtr todo_block_full (nat size, gen_workspace *ws) { @@ -193,17 +224,7 @@ todo_block_full (nat size, gen_workspace *ws) // We can extend the limit for the current block if there's enough // room for the current object, *and* we're not into the second or - // subsequent block of a large block. The second condition occurs - // when we evacuate an object that is larger than a block. In - // that case, alloc_todo_block() sets todo_lim to be exactly the - // size of the large object, and we don't evacuate any more - // objects into this block. The reason is that the rest of the GC - // is not set up to handle objects that start in the second or - // later blocks of a group. We just about manage this in the - // nursery (see scheduleHandleHeapOverflow()) so evacuate() can - // handle this, but other parts of the GC can't. We could - // probably fix this, but it's a rare case anyway. - // + // subsequent block of a large block (see Note [big objects]). can_extend = ws->todo_free + size <= bd->start + bd->blocks * BLOCK_SIZE_W && ws->todo_free < ws->todo_bd->start + BLOCK_SIZE_W; @@ -316,6 +337,7 @@ alloc_todo_block (gen_workspace *ws, nat size) ws->todo_free = bd->free; ws->todo_lim = stg_min(bd->start + bd->blocks * BLOCK_SIZE_W, bd->free + stg_max(WORK_UNIT_WORDS,size)); + // See Note [big objects] debugTrace(DEBUG_gc, "alloc new todo block %p for gen %d", bd->free, ws->gen->no); diff --git a/testsuite/tests/rts/all.T b/testsuite/tests/rts/all.T index 0e891e8f1b..72566d1fd0 100644 --- a/testsuite/tests/rts/all.T +++ b/testsuite/tests/rts/all.T @@ -224,7 +224,6 @@ test('ffishutdown', [ ignore_output, only_ways(['threaded1','threaded2']) ], com test('T7919', [extra_clean(['T7919A.o','T7919A.hi', 'T7919A.dyn_o','T7919A.dyn_hi']), - expect_broken_for(7919, ['optasm','dyn','optllvm']), when(fast(),skip) ], compile_and_run, [config.ghc_th_way_flags]) |