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remove "low memory" heuristic from heap code

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The original goal was to minimize memory usage by garbage collecting
more frequently and more comprehensively as we got closer to the heap
limit.  In practice, though, this just slowed the VM to a crawl as
memory pressure increased.  If an app really wants to use a lot of
memory, the VM shouldn't penalize it aside from throwing an
OutOfMemoryError if it exceeds the limit.
This commit is contained in:
Joel Dice 2013-03-04 16:02:59 -07:00
parent 3209f8750a
commit c6185c8034
1 changed files with 6 additions and 45 deletions
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51
src/heap/heap.cpp
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@ -27,8 +27,6 @@ const unsigned Top = ~static_cast<unsigned>(0);
const unsigned InitialGen2CapacityInBytes = 4 * 1024 * 1024;
const unsigned InitialTenuredFixieCeilingInBytes = 4 * 1024 * 1024;
const unsigned LowMemoryPaddingInBytes = 1024 * 1024;
const bool Verbose = false;
const bool Verbose2 = false;
const bool Debug = false;
@ -62,6 +60,7 @@ Aborter* getAborter(Context* c);
void* tryAllocate(Context* c, unsigned size);
void* allocate(Context* c, unsigned size);
void* allocate(Context* c, unsigned size, bool limit);
void free(Context* c, const void* p, unsigned size);
#ifdef USE_ATOMIC_OPERATIONS
@ -348,7 +347,8 @@ class Segment {
capacity_ = desired;
while (data == 0) {
data = static_cast<uintptr_t*>
(tryAllocate(context, (footprint(capacity_)) * BytesPerWord));
(local::allocate
(context, (footprint(capacity_)) * BytesPerWord, false));
if (data == 0) {
if (capacity_ > minimum) {
@ -609,7 +609,6 @@ class Context {
client(0),
count(0),
limit(limit),
lowMemoryThreshold(limit / 2),
lock(0),
immortalHeapStart(0),
@ -680,7 +679,6 @@ class Context {
unsigned count;
unsigned limit;
unsigned lowMemoryThreshold;
System::Mutex* lock;
@ -770,21 +768,6 @@ oversizedGen2(Context* c)
and c->gen2.position() < (c->gen2.capacity() / 4);
}
inline unsigned
memoryNeeded(Context* c)
{
return c->count
+ ((c->gen1.footprint(minimumNextGen1Capacity(c))
+ c->gen2.footprint(minimumNextGen2Capacity(c))) * BytesPerWord)
+ LowMemoryPaddingInBytes;
}
inline bool
lowMemory(Context* c)
{
return memoryNeeded(c) > c->lowMemoryThreshold;
}
inline void
initNextGen1(Context* c)
{
@ -818,7 +801,7 @@ initNextGen2(Context* c)
unsigned minimum = minimumNextGen2Capacity(c);
unsigned desired = minimum;
if (not (lowMemory(c) or oversizedGen2(c))) {
if (not oversizedGen2(c)) {
desired *= 2;
}
@ -1666,16 +1649,13 @@ collect2(Context* c)
void
collect(Context* c)
{
if (lowMemory(c)
or oversizedGen2(c)
if (oversizedGen2(c)
or c->tenureFootprint + c->tenurePadding > c->gen2.remaining()
or c->fixieTenureFootprint + c->tenuredFixieFootprint
> c->tenuredFixieCeiling)
{
if (Verbose) {
if (lowMemory(c)) {
fprintf(stderr, "low memory causes ");
} else if (oversizedGen2(c)) {
if (oversizedGen2(c)) {
fprintf(stderr, "oversized gen2 causes ");
} else if (c->tenureFootprint + c->tenurePadding > c->gen2.remaining())
{
@ -1699,25 +1679,6 @@ collect(Context* c)
then = c->system->now();
}
unsigned count = memoryNeeded(c);
if (count > c->lowMemoryThreshold) {
if (Verbose) {
fprintf(stderr, "increase low memory threshold from %d to %d\n",
c->lowMemoryThreshold,
avg(c->limit, c->lowMemoryThreshold));
}
c->lowMemoryThreshold = avg(c->limit, c->lowMemoryThreshold);
} else if (count + (count / 16) < c->lowMemoryThreshold) {
if (Verbose) {
fprintf(stderr, "decrease low memory threshold from %d to %d\n",
c->lowMemoryThreshold,
avg(count, c->lowMemoryThreshold));
}
c->lowMemoryThreshold = avg(count, c->lowMemoryThreshold);
}
initNextGen1(c);
if (c->mode == Heap::MajorCollection) {