Fix CNF handling in compacting GC (39075176) · Commits · Reinier Maas / GHC

Commit 39075176 authored 4 years ago by Ömer Sinan Ağacan Committed by Marge Bot 4 years ago

Fix CNF handling in compacting GC

Fixes #17937

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:

--------------------------------------------------------------------------------
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%

Bumping numbers of nonsensical perf tests:

Metric Increase:
T12150
T12234
T12425
T13035
T5837
T6048

It's simply not possible for this patch to increase allocations, and
I've wasted enough time on these test in the past (see #17686). I think
these tests should not be perf tests, but for now I'll bump the numbers.

parent fa66f143

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