Skip to content

Commit

Permalink
[scudo] Separated committed and decommitted entries. (#100818)
Browse files Browse the repository at this point in the history 
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 are 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, valid-fit, committed entries (not necessarily optimal-fit)
are retrieved before optimal-fit, decommitted entries.
  • Loading branch information
@JoshuaMBa
JoshuaMBa authored Jul 31, 2024
1 parent 2a6268d commit 8b2688b
Showing 1 changed file with 157 additions and 92 deletions.
249 changes: 157 additions & 92 deletions compiler-rt/lib/scudo/standalone/secondary.h
View file
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 @@ -310,15 +325,19 @@ template <typename Config> class MapAllocatorCache {
// All excess entries are evicted from the cache
while (needToEvict()) {
// Save MemMaps of evicted entries to perform unmap outside of lock
EvictionMemMaps.push_back(Entries[LRUTail].MemMap);
remove(LRUTail);
EntryListT EvictionListType;
if (EntryLists[DECOMMITTED].Tail == CachedBlock::InvalidEntry)
EvictionListType = COMMITTED;
else
EvictionListType = DECOMMITTED;
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 @@ -335,56 +354,69 @@ 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;
uptr OptimalFitIndex = CachedBlock::InvalidEntry;
{
ScopedLock L(Mutex);
CallsToRetrieve++;
if (EntriesCount == 0)
return false;
u32 OptimalFitIndex = 0;
uptr MinDiff = UINTPTR_MAX;
for (u32 I = LRUHead; I != CachedBlock::InvalidEntry;
I = Entries[I].Next) {
const uptr CommitBase = Entries[I].CommitBase;
const uptr CommitSize = Entries[I].CommitSize;
const uptr AllocPos =
roundDown(CommitBase + CommitSize - Size, Alignment);
const uptr HeaderPos = AllocPos - HeadersSize;
if (HeaderPos > CommitBase + CommitSize)
continue;
if (HeaderPos < CommitBase ||
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.
const uptr MaxAllowedFragmentedBytes =
(CommitBase + CommitSize - HeaderPos) / FragmentedBytesDivisor;
if (Diff <= MaxAllowedFragmentedBytes) {
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;
const uptr AllocPos =
roundDown(CommitBase + CommitSize - Size, Alignment);
const uptr HeaderPos = AllocPos - HeadersSize;
if (HeaderPos > CommitBase + CommitSize)
continue;
if (HeaderPos < CommitBase ||
AllocPos > CommitBase + PageSize * MaxUnusedCachePages)
continue;

const uptr Diff = HeaderPos - CommitBase;
// 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;
OptimalFitListType = ListType;
return Entries[OptimalFitIndex];
}

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

// Prioritize valid fit from COMMITTED entries over
// optimal fit from DECOMMITTED entries
Entry = FindAvailableEntry(COMMITTED);
if (!Entry.isValid())
Entry = FindAvailableEntry(DECOMMITTED);

if (!Entry.isValid())
return false;

remove(OptimalFitIndex, OptimalFitListType);
SuccessfulRetrieves++;
} // ScopedLock L(Mutex);

*H = reinterpret_cast<LargeBlock::Header *>(
LargeBlock::addHeaderTag<Config>(EntryHeaderPos));
Expand Down Expand Up @@ -448,10 +480,15 @@ 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[COMMITTED].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 +503,7 @@ 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 @@ -475,71 +512,92 @@ 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 < N; I++) {
MemMapT &MemMap = MapInfo[I];
MemMap.unmap(MemMap.getBase(), MemMap.getCapacity());
}

for (uptr I = 0; I < Config::getEntriesArraySize(); I++)
DCHECK(!Entries[I].isValid());
}

void releaseIfOlderThan(CachedBlock &Entry, u64 Time) REQUIRES(Mutex) {
Expand All @@ -561,8 +619,13 @@ 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 (uptr I = 0; I < Config::getEntriesArraySize(); I++) {
if (Entries[I].isValid() && Entries[I].Time && Entries[I].Time <= Time) {
unlink(I, COMMITTED);
pushFront(I, DECOMMITTED);
}
releaseIfOlderThan(Entries[I], Time);
}
}

HybridMutex Mutex;
Expand All @@ -579,10 +642,12 @@ 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 are those that are not madvise()'d
// DECOMMITTED entries are those that are madvise()'d
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

0 comments on commit 8b2688b

Please sign in to comment.