Fix CNF handling in compacting GC
Fixes #17937 (closed)
Previously compacting GC simply ignored CNFs. This is mostly fine as most (see "What about small compacts?" below) CNF objects don't have outgoing pointers, and are "large" (allocated in large blocks) and large objects are not moved or compacted.
However if we do GC during sharing-preserving compaction then the CNF will have a hash table mapping objects that have been moved to the CNF to their location in the CNF, to be able to preserve sharing.
This case is handled in the copying collector, in scavenge_compact,
where we evacuate hash table entries and then rehash the table.
Compacting GC ignored this case.
We now visit CNFs in all generations when threading pointers to the
compacted heap and thread hash table keys. A visited CNF is added to the
list nfdata_chain. After compaction is done, we re-visit the CNFs in
that list and rehash the tables.
The overhead is minimal: the list is static in Compact.c, and link
field is added to StgCompactNFData closure. Programs that don't use
CNFs should not be affected.
To test this CNF tests are now also run in a new way 'compacting_gc',
which just passes -c to the RTS, enabling compacting GC for the oldest
generation. Before this patch the result would be:
Unexpected failures:
compact_gc.run compact_gc [bad exit code (139)] (compacting_gc)
compact_huge_array.run compact_huge_array [bad exit code (1)] (compacting_gc)With this patch all tests pass. I can also pass -c -DS without any
failures.
What about small compacts? Small CNFs are still not handled by the compacting GC. However so far I'm unable to write a test that triggers a runtime panic ("update_fwd: unknown/strange object") by allocating a small CNF in a compated heap. It's possible that I'm missing something and it's not possible to have a small CNF.
NoFib results:
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Program Size Allocs Instrs Reads Writes
--------------------------------------------------------------------------------
CS +0.1% 0.0% 0.0% +0.0% +0.0%
CSD +0.1% 0.0% 0.0% 0.0% 0.0%
FS +0.1% 0.0% 0.0% 0.0% 0.0%
S +0.1% 0.0% 0.0% 0.0% 0.0%
VS +0.1% 0.0% 0.0% 0.0% 0.0%
VSD +0.1% 0.0% +0.0% +0.0% -0.0%
VSM +0.1% 0.0% +0.0% -0.0% 0.0%
anna +0.0% 0.0% -0.0% -0.0% -0.0%
ansi +0.1% 0.0% +0.0% +0.0% +0.0%
atom +0.1% 0.0% +0.0% +0.0% +0.0%
awards +0.1% 0.0% +0.0% +0.0% +0.0%
banner +0.1% 0.0% +0.0% +0.0% +0.0%
bernouilli +0.1% 0.0% 0.0% -0.0% +0.0%
binary-trees +0.1% 0.0% -0.0% -0.0% 0.0%
boyer +0.1% 0.0% +0.0% +0.0% +0.0%
boyer2 +0.1% 0.0% +0.0% +0.0% +0.0%
bspt +0.1% 0.0% -0.0% -0.0% -0.0%
cacheprof +0.1% 0.0% -0.0% -0.0% -0.0%
calendar +0.1% 0.0% +0.0% +0.0% +0.0%
cichelli +0.1% 0.0% +0.0% +0.0% +0.0%
circsim +0.1% 0.0% +0.0% +0.0% +0.0%
clausify +0.1% 0.0% -0.0% +0.0% +0.0%
comp_lab_zift +0.1% 0.0% +0.0% +0.0% +0.0%
compress +0.1% 0.0% +0.0% +0.0% 0.0%
compress2 +0.1% 0.0% -0.0% 0.0% 0.0%
constraints +0.1% 0.0% +0.0% +0.0% +0.0%
cryptarithm1 +0.1% 0.0% +0.0% +0.0% +0.0%
cryptarithm2 +0.1% 0.0% +0.0% +0.0% +0.0%
cse +0.1% 0.0% +0.0% +0.0% +0.0%
digits-of-e1 +0.1% 0.0% +0.0% -0.0% -0.0%
digits-of-e2 +0.1% 0.0% -0.0% -0.0% -0.0%
dom-lt +0.1% 0.0% +0.0% +0.0% +0.0%
eliza +0.1% 0.0% +0.0% +0.0% +0.0%
event +0.1% 0.0% +0.0% +0.0% +0.0%
exact-reals +0.1% 0.0% +0.0% +0.0% +0.0%
exp3_8 +0.1% 0.0% +0.0% -0.0% 0.0%
expert +0.1% 0.0% +0.0% +0.0% +0.0%
fannkuch-redux +0.1% 0.0% -0.0% 0.0% 0.0%
fasta +0.1% 0.0% -0.0% +0.0% +0.0%
fem +0.1% 0.0% -0.0% +0.0% 0.0%
fft +0.1% 0.0% -0.0% +0.0% +0.0%
fft2 +0.1% 0.0% +0.0% +0.0% +0.0%
fibheaps +0.1% 0.0% +0.0% +0.0% +0.0%
fish +0.1% 0.0% +0.0% +0.0% +0.0%
fluid +0.0% 0.0% +0.0% +0.0% +0.0%
fulsom +0.1% 0.0% -0.0% +0.0% 0.0%
gamteb +0.1% 0.0% +0.0% +0.0% 0.0%
gcd +0.1% 0.0% +0.0% +0.0% +0.0%
gen_regexps +0.1% 0.0% -0.0% +0.0% 0.0%
genfft +0.1% 0.0% +0.0% +0.0% +0.0%
gg +0.1% 0.0% 0.0% +0.0% +0.0%
grep +0.1% 0.0% -0.0% +0.0% +0.0%
hidden +0.1% 0.0% +0.0% -0.0% 0.0%
hpg +0.1% 0.0% -0.0% -0.0% -0.0%
ida +0.1% 0.0% +0.0% +0.0% +0.0%
infer +0.1% 0.0% +0.0% 0.0% -0.0%
integer +0.1% 0.0% +0.0% +0.0% +0.0%
integrate +0.1% 0.0% -0.0% -0.0% -0.0%
k-nucleotide +0.1% 0.0% +0.0% +0.0% 0.0%
kahan +0.1% 0.0% +0.0% +0.0% +0.0%
knights +0.1% 0.0% -0.0% -0.0% -0.0%
lambda +0.1% 0.0% +0.0% +0.0% -0.0%
last-piece +0.1% 0.0% +0.0% 0.0% 0.0%
lcss +0.1% 0.0% +0.0% +0.0% 0.0%
life +0.1% 0.0% -0.0% +0.0% +0.0%
lift +0.1% 0.0% +0.0% +0.0% +0.0%
linear +0.1% 0.0% -0.0% +0.0% 0.0%
listcompr +0.1% 0.0% +0.0% +0.0% +0.0%
listcopy +0.1% 0.0% +0.0% +0.0% +0.0%
maillist +0.1% 0.0% +0.0% -0.0% -0.0%
mandel +0.1% 0.0% +0.0% +0.0% 0.0%
mandel2 +0.1% 0.0% +0.0% +0.0% +0.0%
mate +0.1% 0.0% +0.0% 0.0% +0.0%
minimax +0.1% 0.0% -0.0% 0.0% -0.0%
mkhprog +0.1% 0.0% +0.0% +0.0% +0.0%
multiplier +0.1% 0.0% +0.0% 0.0% 0.0%
n-body +0.1% 0.0% +0.0% +0.0% +0.0%
nucleic2 +0.1% 0.0% +0.0% +0.0% +0.0%
para +0.1% 0.0% 0.0% +0.0% +0.0%
paraffins +0.1% 0.0% +0.0% -0.0% 0.0%
parser +0.1% 0.0% -0.0% -0.0% -0.0%
parstof +0.1% 0.0% +0.0% +0.0% +0.0%
pic +0.1% 0.0% -0.0% -0.0% 0.0%
pidigits +0.1% 0.0% +0.0% -0.0% -0.0%
power +0.1% 0.0% +0.0% +0.0% +0.0%
pretty +0.1% 0.0% -0.0% -0.0% -0.1%
primes +0.1% 0.0% -0.0% -0.0% -0.0%
primetest +0.1% 0.0% -0.0% -0.0% -0.0%
prolog +0.1% 0.0% -0.0% -0.0% -0.0%
puzzle +0.1% 0.0% -0.0% -0.0% -0.0%
queens +0.1% 0.0% +0.0% +0.0% +0.0%
reptile +0.1% 0.0% -0.0% -0.0% +0.0%
reverse-complem +0.1% 0.0% +0.0% 0.0% -0.0%
rewrite +0.1% 0.0% -0.0% -0.0% -0.0%
rfib +0.1% 0.0% +0.0% +0.0% +0.0%
rsa +0.1% 0.0% -0.0% +0.0% -0.0%
scc +0.1% 0.0% -0.0% -0.0% -0.1%
sched +0.1% 0.0% +0.0% +0.0% +0.0%
scs +0.1% 0.0% +0.0% +0.0% +0.0%
simple +0.1% 0.0% -0.0% -0.0% -0.0%
solid +0.1% 0.0% +0.0% +0.0% +0.0%
sorting +0.1% 0.0% -0.0% -0.0% -0.0%
spectral-norm +0.1% 0.0% +0.0% +0.0% +0.0%
sphere +0.1% 0.0% -0.0% -0.0% -0.0%
symalg +0.1% 0.0% -0.0% -0.0% -0.0%
tak +0.1% 0.0% +0.0% +0.0% +0.0%
transform +0.1% 0.0% +0.0% +0.0% +0.0%
treejoin +0.1% 0.0% +0.0% -0.0% -0.0%
typecheck +0.1% 0.0% +0.0% +0.0% +0.0%
veritas +0.0% 0.0% +0.0% +0.0% +0.0%
wang +0.1% 0.0% 0.0% +0.0% +0.0%
wave4main +0.1% 0.0% +0.0% +0.0% +0.0%
wheel-sieve1 +0.1% 0.0% +0.0% +0.0% +0.0%
wheel-sieve2 +0.1% 0.0% +0.0% +0.0% +0.0%
x2n1 +0.1% 0.0% +0.0% +0.0% +0.0%
--------------------------------------------------------------------------------
Min +0.0% 0.0% -0.0% -0.0% -0.1%
Max +0.1% 0.0% +0.0% +0.0% +0.0%
Geometric Mean +0.1% -0.0% -0.0% -0.0% -0.0%