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[scudo] Separated committed and decommitted entries.
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Initially, the LRU list stored all mapped entries with no distinction
between the committed (non-madvise()'d) entries and decommitted (madvise()'d)
entries. Now these two types of entries re separated into two lists, allowing
future cache logic to branch depending on whether or not entries are committed
or decommitted. Furthermore, the retrieval algorithm will prioritize committed
entries over decommitted entries. Specifically, committed entries that
satisfy the MaxUnusedCachePages requirement are retrieved before optimal-fit,
decommitted entries.
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@JoshuaMBa
JoshuaMBa committed Aug 2, 2024
1 parent 30b5d4a commit 4d028c9
Showing 1 changed file with 139 additions and 76 deletions.
215 changes: 139 additions & 76 deletions compiler-rt/lib/scudo/standalone/secondary.h
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Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,14 @@ template <typename T> class NonZeroLengthArray<T, 0> {

template <typename Config> class MapAllocatorCache {
public:
typedef enum { COMMITTED = 0, DECOMMITTED = 1, NONE } EntryListT;

// TODO: Refactor the intrusive list to support non-pointer link type
typedef struct {
u16 Head;
u16 Tail;
} ListInfo;

void getStats(ScopedString *Str) {
ScopedLock L(Mutex);
uptr Integral;
Expand All @@ -197,13 +205,18 @@ template <typename Config> class MapAllocatorCache {
SuccessfulRetrieves, CallsToRetrieve, Integral, Fractional);
Str->append("Cache Entry Info (Most Recent -> Least Recent):\n");

for (u32 I = LRUHead; I != CachedBlock::InvalidEntry; I = Entries[I].Next) {
CachedBlock &Entry = Entries[I];
Str->append(" StartBlockAddress: 0x%zx, EndBlockAddress: 0x%zx, "
"BlockSize: %zu %s\n",
Entry.CommitBase, Entry.CommitBase + Entry.CommitSize,
Entry.CommitSize, Entry.Time == 0 ? "[R]" : "");
}
auto printList = [&](EntryListT ListType) REQUIRES(Mutex) {
for (u32 I = EntryLists[ListType].Head; I != CachedBlock::InvalidEntry;
I = Entries[I].Next) {
CachedBlock &Entry = Entries[I];
Str->append(" StartBlockAddress: 0x%zx, EndBlockAddress: 0x%zx, "
"BlockSize: %zu %s\n",
Entry.CommitBase, Entry.CommitBase + Entry.CommitSize,
Entry.CommitSize, Entry.Time == 0 ? "[R]" : "");
}
};
printList(COMMITTED);
printList(DECOMMITTED);
}

// Ensure the default maximum specified fits the array.
Expand All @@ -227,8 +240,10 @@ template <typename Config> class MapAllocatorCache {
setOption(Option::ReleaseInterval, static_cast<sptr>(ReleaseToOsInterval));

// The cache is initially empty
LRUHead = CachedBlock::InvalidEntry;
LRUTail = CachedBlock::InvalidEntry;
EntryLists[COMMITTED].Head = CachedBlock::InvalidEntry;
EntryLists[COMMITTED].Tail = CachedBlock::InvalidEntry;
EntryLists[DECOMMITTED].Head = CachedBlock::InvalidEntry;
EntryLists[DECOMMITTED].Tail = CachedBlock::InvalidEntry;

// Available entries will be retrieved starting from the beginning of the
// Entries array
Expand Down Expand Up @@ -309,16 +324,22 @@ template <typename Config> class MapAllocatorCache {

// All excess entries are evicted from the cache
while (needToEvict()) {
EntryListT EvictionListType;
if (EntryLists[DECOMMITTED].Tail == CachedBlock::InvalidEntry)
EvictionListType = COMMITTED;
else
EvictionListType = DECOMMITTED;
// Save MemMaps of evicted entries to perform unmap outside of lock
EvictionMemMaps.push_back(Entries[LRUTail].MemMap);
remove(LRUTail);
EvictionMemMaps.push_back(
Entries[EntryLists[EvictionListType].Tail].MemMap);
remove(EntryLists[EvictionListType].Tail, EvictionListType);
}

insert(Entry);
insert(Entry, (Entry.Time == 0) ? DECOMMITTED : COMMITTED);

if (OldestTime == 0)
OldestTime = Entry.Time;
} while (0);
} while (0); // ScopedLock L(Mutex);

for (MemMapT &EvictMemMap : EvictionMemMaps)
EvictMemMap.unmap(EvictMemMap.getBase(), EvictMemMap.getCapacity());
Expand All @@ -335,17 +356,14 @@ template <typename Config> class MapAllocatorCache {
// 10% of the requested size proved to be the optimal choice for
// retrieving cached blocks after testing several options.
constexpr u32 FragmentedBytesDivisor = 10;
bool Found = false;
CachedBlock Entry;
uptr EntryHeaderPos = 0;
{
ScopedLock L(Mutex);
CallsToRetrieve++;
if (EntriesCount == 0)
return false;
u32 OptimalFitIndex = 0;
uptr MinDiff = UINTPTR_MAX;
for (u32 I = LRUHead; I != CachedBlock::InvalidEntry;
uptr OptimalFitIndex = CachedBlock::InvalidEntry;
uptr MinDiff = UINTPTR_MAX;
EntryListT OptimalFitListType = NONE;

auto FindAvailableEntry = [&](EntryListT ListType) REQUIRES(Mutex) {
for (uptr I = EntryLists[ListType].Head; I != CachedBlock::InvalidEntry;
I = Entries[I].Next) {
const uptr CommitBase = Entries[I].CommitBase;
const uptr CommitSize = Entries[I].CommitSize;
Expand All @@ -355,36 +373,48 @@ template <typename Config> class MapAllocatorCache {
if (HeaderPos > CommitBase + CommitSize)
continue;
if (HeaderPos < CommitBase ||
AllocPos > CommitBase + PageSize * MaxUnusedCachePages) {
AllocPos > CommitBase + PageSize * MaxUnusedCachePages)
continue;
}
Found = true;

const uptr Diff = HeaderPos - CommitBase;
// immediately use a cached block if it's size is close enough to the
// requested size.
// immediately use a cached block if it's size is close enough to
// the requested size.
const uptr MaxAllowedFragmentedBytes =
(CommitBase + CommitSize - HeaderPos) / FragmentedBytesDivisor;
if (Diff <= MaxAllowedFragmentedBytes) {
OptimalFitIndex = I;
EntryHeaderPos = HeaderPos;
break;
OptimalFitListType = ListType;
return true;
}

// keep track of the smallest cached block
// that is greater than (AllocSize + HeaderSize)
if (Diff > MinDiff)
continue;
OptimalFitIndex = I;
MinDiff = Diff;
OptimalFitListType = ListType;
EntryHeaderPos = HeaderPos;
}
if (Found) {
Entry = Entries[OptimalFitIndex];
remove(OptimalFitIndex);
SuccessfulRetrieves++;
}
}
if (!Found)
return false;
return (OptimalFitIndex != CachedBlock::InvalidEntry);
};

{
ScopedLock L(Mutex);
CallsToRetrieve++;
if (EntriesCount == 0)
return false;

// Prioritize valid fit from COMMITTED entries over
// optimal fit from DECOMMITTED entries
if (!FindAvailableEntry(COMMITTED) && !FindAvailableEntry(DECOMMITTED))
return false;

Entry = Entries[OptimalFitIndex];
remove(OptimalFitIndex, OptimalFitListType);
SuccessfulRetrieves++;
} // ScopedLock L(Mutex);

*H = reinterpret_cast<LargeBlock::Header *>(
LargeBlock::addHeaderTag<Config>(EntryHeaderPos));
Expand Down Expand Up @@ -448,10 +478,15 @@ template <typename Config> class MapAllocatorCache {
Quarantine[I].invalidate();
}
}
for (u32 I = LRUHead; I != CachedBlock::InvalidEntry; I = Entries[I].Next) {
Entries[I].MemMap.setMemoryPermission(Entries[I].CommitBase,
Entries[I].CommitSize, 0);
}
auto disableLists = [&](EntryListT EntryList) REQUIRES(Mutex) {
for (u32 I = EntryLists[EntryList].Head; I != CachedBlock::InvalidEntry;
I = Entries[I].Next) {
Entries[I].MemMap.setMemoryPermission(Entries[I].CommitBase,
Entries[I].CommitSize, 0);
}
};
disableLists(COMMITTED);
disableLists(DECOMMITTED);
QuarantinePos = -1U;
}

Expand All @@ -466,7 +501,7 @@ template <typename Config> class MapAllocatorCache {
return (EntriesCount >= atomic_load_relaxed(&MaxEntriesCount));
}

void insert(const CachedBlock &Entry) REQUIRES(Mutex) {
void insert(const CachedBlock &Entry, EntryListT ListType) REQUIRES(Mutex) {
DCHECK_LT(EntriesCount, atomic_load_relaxed(&MaxEntriesCount));

// Cache should be populated with valid entries when not empty
Expand All @@ -475,66 +510,86 @@ template <typename Config> class MapAllocatorCache {
u32 FreeIndex = AvailableHead;
AvailableHead = Entries[AvailableHead].Next;

if (EntriesCount == 0) {
LRUTail = static_cast<u16>(FreeIndex);
} else {
// Check list order
if (EntriesCount > 1)
DCHECK_GE(Entries[LRUHead].Time, Entries[Entries[LRUHead].Next].Time);
Entries[LRUHead].Prev = static_cast<u16>(FreeIndex);
}

Entries[FreeIndex] = Entry;
Entries[FreeIndex].Next = LRUHead;
Entries[FreeIndex].Prev = CachedBlock::InvalidEntry;
LRUHead = static_cast<u16>(FreeIndex);
pushFront(FreeIndex, ListType);
EntriesCount++;

if (Entries[EntryLists[ListType].Head].Next != CachedBlock::InvalidEntry) {
DCHECK_GE(Entries[EntryLists[ListType].Head].Time,
Entries[Entries[EntryLists[ListType].Head].Next].Time);
}
// Availability stack should not have available entries when all entries
// are in use
if (EntriesCount == Config::getEntriesArraySize())
DCHECK_EQ(AvailableHead, CachedBlock::InvalidEntry);
}

void remove(uptr I) REQUIRES(Mutex) {
DCHECK(Entries[I].isValid());

Entries[I].invalidate();

if (I == LRUHead)
LRUHead = Entries[I].Next;
// Joins the entries adjacent to Entries[I], effectively
// unlinking Entries[I] from the list
void unlink(uptr I, EntryListT ListType) REQUIRES(Mutex) {
if (I == EntryLists[ListType].Head)
EntryLists[ListType].Head = Entries[I].Next;
else
Entries[Entries[I].Prev].Next = Entries[I].Next;

if (I == LRUTail)
LRUTail = Entries[I].Prev;
if (I == EntryLists[ListType].Tail)
EntryLists[ListType].Tail = Entries[I].Prev;
else
Entries[Entries[I].Next].Prev = Entries[I].Prev;
}

// Invalidates Entries[I], removes Entries[I] from list, and pushes
// Entries[I] onto the stack of available entries
void remove(uptr I, EntryListT ListType) REQUIRES(Mutex) {
DCHECK(Entries[I].isValid());

Entries[I].invalidate();

unlink(I, ListType);
Entries[I].Next = AvailableHead;
AvailableHead = static_cast<u16>(I);
EntriesCount--;

// Cache should not have valid entries when not empty
if (EntriesCount == 0) {
DCHECK_EQ(LRUHead, CachedBlock::InvalidEntry);
DCHECK_EQ(LRUTail, CachedBlock::InvalidEntry);
DCHECK_EQ(EntryLists[COMMITTED].Head, CachedBlock::InvalidEntry);
DCHECK_EQ(EntryLists[COMMITTED].Tail, CachedBlock::InvalidEntry);
DCHECK_EQ(EntryLists[DECOMMITTED].Head, CachedBlock::InvalidEntry);
DCHECK_EQ(EntryLists[DECOMMITTED].Tail, CachedBlock::InvalidEntry);
}
}

inline void pushFront(uptr I, EntryListT ListType) REQUIRES(Mutex) {
if (EntryLists[ListType].Tail == CachedBlock::InvalidEntry)
EntryLists[ListType].Tail = static_cast<u16>(I);
else
Entries[EntryLists[ListType].Head].Prev = static_cast<u16>(I);

Entries[I].Next = EntryLists[ListType].Head;
Entries[I].Prev = CachedBlock::InvalidEntry;
EntryLists[ListType].Head = static_cast<u16>(I);
}

void empty() {
MemMapT MapInfo[Config::getEntriesArraySize()];
uptr N = 0;
{
ScopedLock L(Mutex);
for (uptr I = 0; I < Config::getEntriesArraySize(); I++) {
if (!Entries[I].isValid())
continue;
MapInfo[N] = Entries[I].MemMap;
remove(I);
N++;
}
auto emptyList = [&](EntryListT ListType) REQUIRES(Mutex) {
for (uptr I = EntryLists[ListType].Head;
I != CachedBlock::InvalidEntry;) {
uptr ToRemove = I;
I = Entries[I].Next;
MapInfo[N] = Entries[ToRemove].MemMap;
remove(ToRemove, ListType);
N++;
}
};
emptyList(COMMITTED);
emptyList(DECOMMITTED);
EntriesCount = 0;
for (uptr I = 0; I < Config::getEntriesArraySize(); I++)
DCHECK(!Entries[I].isValid());
}
for (uptr I = 0; I < N; I++) {
MemMapT &MemMap = MapInfo[I];
Expand All @@ -561,8 +616,14 @@ template <typename Config> class MapAllocatorCache {
OldestTime = 0;
for (uptr I = 0; I < Config::getQuarantineSize(); I++)
releaseIfOlderThan(Quarantine[I], Time);
for (uptr I = 0; I < Config::getEntriesArraySize(); I++)
for (u16 I = EntryLists[COMMITTED].Head; I != CachedBlock::InvalidEntry;
I = Entries[I].Next) {
if (Entries[I].Time && Entries[I].Time <= Time) {
unlink(I, COMMITTED);
pushFront(I, DECOMMITTED);
}
releaseIfOlderThan(Entries[I], Time);
}
}

HybridMutex Mutex;
Expand All @@ -579,10 +640,12 @@ template <typename Config> class MapAllocatorCache {
NonZeroLengthArray<CachedBlock, Config::getQuarantineSize()>
Quarantine GUARDED_BY(Mutex) = {};

// The LRUHead of the cache is the most recently used cache entry
u16 LRUHead GUARDED_BY(Mutex) = 0;
// The LRUTail of the cache is the least recently used cache entry
u16 LRUTail GUARDED_BY(Mutex) = 0;
// EntryLists stores the head and tail indices of all
// lists being used to store valid cache entries.
// Currently there are lists storing COMMITTED and DECOMMITTED entries.
// COMMITTED entries have memory chunks that have not been released to the OS
// DECOMMITTED entries have memory chunks that have been released to the OS
ListInfo EntryLists[2] GUARDED_BY(Mutex) = {};
// The AvailableHead is the top of the stack of available entries
u16 AvailableHead GUARDED_BY(Mutex) = 0;
};
Expand Down

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