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Even more HyperClockCache refactoring (#11630)

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Summary:
... ahead of dynamic variant.

* Introduce an Unref function for a common pattern. Cases that were previously using std::memory_order_acq_rel we doing so because we were saving the pre-updated value in case it might be used. Now we are explicitly throwing away the pre-updated value so do not need the acquire semantic, just release.
* Introduce a reusable EvictionData struct and TrackAndReleaseEvictedEntry() function.
* Based on a linter suggesting, use const Func& parameter type instead of Func for templated callable parameters.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11630

Test Plan: existing tests, and performance test with release build of cache_bench. Getting 1-2% difference between before & after from run to run, but inconsistent about which one is faster.

Reviewed By: jowlyzhang

Differential Revision: D47657334

Pulled By: pdillinger

fbshipit-source-id: 5cf2377c0d47a39143b04be6735f98c550e8bdc3
oxigraph-main
Peter Dillinger 1 year ago committed by Facebook GitHub Bot
parent 1567108fc1
commit c41122b1a0
2 changed files with 76 additions and 76 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 137
      cache/clock_cache.cc
  2. 15
      cache/clock_cache.h

137
cache/clock_cache.cc vendored
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@ -73,6 +73,16 @@ inline void FreeDataMarkEmpty(ClockHandle& h, MemoryAllocator* allocator) {
MarkEmpty(h);
}
// Called to undo the effect of referencing an entry for internal purposes,
// so it should not be marked as having been used.
inline void Unref(const ClockHandle& h, uint64_t count = 1) {
// Pretend we never took the reference
// WART: there's a tiny chance we release last ref to invisible
// entry here. If that happens, we let eviction take care of it.
h.meta.fetch_sub(ClockHandle::kAcquireIncrement * count,
std::memory_order_release);
}
inline bool ClockUpdate(ClockHandle& h) {
uint64_t meta = h.meta.load(std::memory_order_relaxed);
@ -231,25 +241,18 @@ inline bool BeginSlotInsert(const ClockHandleBasicData& proto, ClockHandle& h,
*already_matches = true;
return false;
} else {
// Mismatch. Pretend we never took the reference
old_meta =
h.meta.fetch_sub(ClockHandle::kAcquireIncrement * initial_countdown,
std::memory_order_acq_rel);
// Mismatch.
Unref(h, initial_countdown);
}
} else if (UNLIKELY((old_meta >> ClockHandle::kStateShift) ==
ClockHandle::kStateInvisible)) {
// Pretend we never took the reference
// WART/FIXME?: there's a tiny chance we release last ref to invisible
// entry here. If that happens, we let eviction take care of it.
old_meta =
h.meta.fetch_sub(ClockHandle::kAcquireIncrement * initial_countdown,
std::memory_order_acq_rel);
Unref(h, initial_countdown);
} else {
// For other states, incrementing the acquire counter has no effect
// so we don't need to undo it.
// Slot not usable / touchable now.
}
(void)old_meta;
return false;
}
@ -289,9 +292,10 @@ bool TryInsert(const ClockHandleBasicData& proto, ClockHandle& h,
return b;
}
// Func must be const HandleImpl& -> void callable
template <class HandleImpl, class Func>
void ConstApplyToEntriesRange(Func /*const HandleImpl& -> void*/ func,
const HandleImpl* begin, const HandleImpl* end,
void ConstApplyToEntriesRange(const Func& func, const HandleImpl* begin,
const HandleImpl* end,
bool apply_if_will_be_deleted) {
uint64_t check_state_mask = ClockHandle::kStateShareableBit;
if (!apply_if_will_be_deleted) {
@ -316,8 +320,7 @@ void ConstApplyToEntriesRange(Func /*const HandleImpl& -> void*/ func,
func(*h);
}
// Pretend we never took the reference
h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
// No net change, so don't need to check for overflow
} else {
// For other states, incrementing the acquire counter has no effect
@ -419,22 +422,20 @@ Status BaseClockTable::ChargeUsageMaybeEvictStrict(
request_evict_charge = 1;
}
if (request_evict_charge > 0) {
size_t evicted_charge = 0;
size_t evicted_count = 0;
static_cast<Table*>(this)->Evict(request_evict_charge, &evicted_charge,
&evicted_count, state);
occupancy_.fetch_sub(evicted_count, std::memory_order_release);
if (LIKELY(evicted_charge > need_evict_charge)) {
assert(evicted_count > 0);
EvictionData data;
static_cast<Table*>(this)->Evict(request_evict_charge, state, &data);
occupancy_.fetch_sub(data.freed_count, std::memory_order_release);
if (LIKELY(data.freed_charge > need_evict_charge)) {
assert(data.freed_count > 0);
// Evicted more than enough
usage_.fetch_sub(evicted_charge - need_evict_charge,
usage_.fetch_sub(data.freed_charge - need_evict_charge,
std::memory_order_relaxed);
} else if (evicted_charge < need_evict_charge ||
(UNLIKELY(need_evict_for_occupancy) && evicted_count == 0)) {
} else if (data.freed_charge < need_evict_charge ||
(UNLIKELY(need_evict_for_occupancy) && data.freed_count == 0)) {
// Roll back to old usage minus evicted
usage_.fetch_sub(evicted_charge + (new_usage - old_usage),
usage_.fetch_sub(data.freed_charge + (new_usage - old_usage),
std::memory_order_relaxed);
if (evicted_charge < need_evict_charge) {
if (data.freed_charge < need_evict_charge) {
return Status::MemoryLimit(
"Insert failed because unable to evict entries to stay within "
"capacity limit.");
@ -446,7 +447,7 @@ Status BaseClockTable::ChargeUsageMaybeEvictStrict(
}
// If we needed to evict something and we are proceeding, we must have
// evicted something.
assert(evicted_count > 0);
assert(data.freed_count > 0);
}
return Status::OK();
}
@ -488,29 +489,47 @@ inline bool BaseClockTable::ChargeUsageMaybeEvictNonStrict(
// deal with occupancy
need_evict_charge = 1;
}
size_t evicted_charge = 0;
size_t evicted_count = 0;
EvictionData data;
if (need_evict_charge > 0) {
static_cast<Table*>(this)->Evict(need_evict_charge, &evicted_charge,
&evicted_count, state);
static_cast<Table*>(this)->Evict(need_evict_charge, state, &data);
// Deal with potential occupancy deficit
if (UNLIKELY(need_evict_for_occupancy) && evicted_count == 0) {
assert(evicted_charge == 0);
if (UNLIKELY(need_evict_for_occupancy) && data.freed_count == 0) {
assert(data.freed_charge == 0);
// Can't meet occupancy requirement
return false;
} else {
// Update occupancy for evictions
occupancy_.fetch_sub(evicted_count, std::memory_order_release);
occupancy_.fetch_sub(data.freed_count, std::memory_order_release);
}
}
// Track new usage even if we weren't able to evict enough
usage_.fetch_add(total_charge - evicted_charge, std::memory_order_relaxed);
usage_.fetch_add(total_charge - data.freed_charge, std::memory_order_relaxed);
// No underflow
assert(usage_.load(std::memory_order_relaxed) < SIZE_MAX / 2);
// Success
return true;
}
void BaseClockTable::TrackAndReleaseEvictedEntry(
ClockHandle* h, BaseClockTable::EvictionData* data) {
data->freed_charge += h->GetTotalCharge();
data->freed_count += 1;
bool took_value_ownership = false;
if (eviction_callback_) {
// For key reconstructed from hash
UniqueId64x2 unhashed;
took_value_ownership =
eviction_callback_(ClockCacheShard<HyperClockTable>::ReverseHash(
h->GetHash(), &unhashed, hash_seed_),
reinterpret_cast<Cache::Handle*>(h));
}
if (!took_value_ownership) {
h->FreeData(allocator_);
}
MarkEmpty(*h);
}
template <class Table>
Status BaseClockTable::Insert(const ClockHandleBasicData& proto,
typename Table::HandleImpl** handle,
@ -800,23 +819,18 @@ HyperClockTable::HandleImpl* HyperClockTable::Lookup(
return true;
} else {
// Mismatch. Pretend we never took the reference
old_meta = h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
}
} else if (UNLIKELY((old_meta >> ClockHandle::kStateShift) ==
ClockHandle::kStateInvisible)) {
// Pretend we never took the reference
// WART: there's a tiny chance we release last ref to invisible
// entry here. If that happens, we let eviction take care of it.
old_meta = h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
} else {
// For other states, incrementing the acquire counter has no effect
// so we don't need to undo it. Furthermore, we cannot safely undo
// it because we did not acquire a read reference to lock the
// entry in a Shareable state.
}
(void)old_meta;
return false;
},
[&](HandleImpl* h) {
@ -941,8 +955,7 @@ void HyperClockTable::Erase(const UniqueId64x2& hashed_key) {
if (refcount > 1) {
// Not last ref at some point in time during this Erase call
// Pretend we never took the reference
h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
break;
} else if (h->meta.compare_exchange_weak(
old_meta,
@ -962,16 +975,12 @@ void HyperClockTable::Erase(const UniqueId64x2& hashed_key) {
}
} else {
// Mismatch. Pretend we never took the reference
h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
}
} else if (UNLIKELY((old_meta >> ClockHandle::kStateShift) ==
ClockHandle::kStateInvisible)) {
// Pretend we never took the reference
// WART: there's a tiny chance we release last ref to invisible
// entry here. If that happens, we let eviction take care of it.
h->meta.fetch_sub(ClockHandle::kAcquireIncrement,
std::memory_order_release);
Unref(*h);
} else {
// For other states, incrementing the acquire counter has no effect
// so we don't need to undo it.
@ -1007,8 +1016,8 @@ void HyperClockTable::EraseUnRefEntries() {
template <typename MatchFn, typename AbortFn, typename UpdateFn>
inline HyperClockTable::HandleImpl* HyperClockTable::FindSlot(
const UniqueId64x2& hashed_key, MatchFn match_fn, AbortFn abort_fn,
UpdateFn update_fn) {
const UniqueId64x2& hashed_key, const MatchFn& match_fn,
const AbortFn& abort_fn, const UpdateFn& update_fn) {
// NOTE: upper 32 bits of hashed_key[0] is used for sharding
//
// We use double-hashing probing. Every probe in the sequence is a
@ -1062,9 +1071,8 @@ inline void HyperClockTable::ReclaimEntryUsage(size_t total_charge) {
assert(old_usage >= total_charge);
}
inline void HyperClockTable::Evict(size_t requested_charge,
size_t* freed_charge, size_t* freed_count,
InsertState&) {
inline void HyperClockTable::Evict(size_t requested_charge, InsertState&,
EvictionData* data) {
// precondition
assert(requested_charge > 0);
@ -1083,33 +1091,18 @@ inline void HyperClockTable::Evict(size_t requested_charge,
uint64_t max_clock_pointer =
old_clock_pointer + (ClockHandle::kMaxCountdown << length_bits_);
// For key reconstructed from hash
UniqueId64x2 unhashed;
for (;;) {
for (size_t i = 0; i < step_size; i++) {
HandleImpl& h = array_[ModTableSize(Lower32of64(old_clock_pointer + i))];
bool evicting = ClockUpdate(h);
if (evicting) {
Rollback(h.hashed_key, &h);
*freed_charge += h.GetTotalCharge();
*freed_count += 1;
bool took_ownership = false;
if (eviction_callback_) {
took_ownership =
eviction_callback_(ClockCacheShard<HyperClockTable>::ReverseHash(
h.GetHash(), &unhashed, hash_seed_),
reinterpret_cast<Cache::Handle*>(&h));
}
if (!took_ownership) {
h.FreeData(allocator_);
}
MarkEmpty(h);
TrackAndReleaseEvictedEntry(&h, data);
}
}
// Loop exit condition
if (*freed_charge >= requested_charge) {
if (data->freed_charge >= requested_charge) {
return;
}
if (old_clock_pointer >= max_clock_pointer) {

15
cache/clock_cache.h vendored
Unescape View File

@ -422,6 +422,13 @@ class BaseClockTable {
uint32_t GetHashSeed() const { return hash_seed_; }
struct EvictionData {
size_t freed_charge = 0;
size_t freed_count = 0;
};
void TrackAndReleaseEvictedEntry(ClockHandle* h, EvictionData* data);
#ifndef NDEBUG
// Acquire N references
void TEST_RefN(ClockHandle& handle, size_t n);
@ -528,8 +535,7 @@ class HyperClockTable : public BaseClockTable {
// Runs the clock eviction algorithm trying to reclaim at least
// requested_charge. Returns how much is evicted, which could be less
// if it appears impossible to evict the requested amount without blocking.
void Evict(size_t requested_charge, size_t* freed_charge, size_t* freed_count,
InsertState& state);
void Evict(size_t requested_charge, InsertState& state, EvictionData* data);
HandleImpl* Lookup(const UniqueId64x2& hashed_key);
@ -570,8 +576,9 @@ class HyperClockTable : public BaseClockTable {
// slot probed. This function uses templates instead of std::function to
// minimize the risk of heap-allocated closures being created.
template <typename MatchFn, typename AbortFn, typename UpdateFn>
inline HandleImpl* FindSlot(const UniqueId64x2& hashed_key, MatchFn match_fn,
AbortFn abort_fn, UpdateFn update_fn);
inline HandleImpl* FindSlot(const UniqueId64x2& hashed_key,
const MatchFn& match_fn, const AbortFn& abort_fn,
const UpdateFn& update_fn);
// Re-decrement all displacements in probe path starting from beginning
// until (not including) the given handle

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