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Improve memory utilization in the case of continuous BGC #87715

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Improve memory utilization in the case of continuous BGC #87715

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d58b0a6
Improve memory utilization in the case of continuous BGC
cshung Jun 16, 2023
47b190a
Avoid taking minimum
cshung Jun 21, 2023
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51 changes: 41 additions & 10 deletions src/coreclr/gc/gc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2332,6 +2332,10 @@ size_t gc_heap::current_total_committed_bookkeeping = 0;

BOOL gc_heap::reset_mm_p = TRUE;

uint32_t gc_heap::uoh_try_fit_segment_end_fail_count = 0;

uint32_t gc_heap::uoh_try_fit_segment_end_count = 0;

#ifdef FEATURE_EVENT_TRACE
bool gc_heap::informational_event_enabled_p = false;

Expand Down Expand Up @@ -13311,7 +13315,12 @@ void gc_heap::distribute_free_regions()
const int i = 0;
const int n_heaps = 1;
#endif //MULTIPLE_HEAPS
ptrdiff_t budget_gen = max (hp->estimate_gen_growth (gen), 0);
#ifdef BACKGROUND_GC
bool bgc_running_p = background_running_p();
#else
bool bgc_running_p = false;
#endif
ptrdiff_t budget_gen = max (hp->estimate_gen_growth (gen, bgc_running_p), 0);
int kind = gen >= loh_generation;
size_t budget_gen_in_region_units = (budget_gen + (region_size[kind] - 1)) / region_size[kind];
dprintf (REGIONS_LOG, ("h%2d gen %d has an estimated growth of %zd bytes (%zd regions)", i, gen, budget_gen, budget_gen_in_region_units));
Expand Down Expand Up @@ -13361,11 +13370,7 @@ void gc_heap::distribute_free_regions()

ptrdiff_t balance = total_num_free_regions[kind] + num_huge_region_units_to_consider[kind] - total_budget_in_region_units[kind];

if (
#ifdef BACKGROUND_GC
background_running_p() ||
#endif
(balance < 0))
if (balance < 0)
{
dprintf (REGIONS_LOG, ("distributing the %zd %s regions deficit", -balance, kind_name[kind]));

Expand Down Expand Up @@ -17499,6 +17504,18 @@ BOOL gc_heap::a_fit_segment_end_p (int gen_number,
int align_const,
BOOL* commit_failed_p)
{
if ((gen_number >= loh_generation) && (heap_segment_allocated(seg) != heap_segment_mem(seg)))
{
// Here we wanted to estimate the probability of the end of a region can fit allocation.
// We knew that it always do for new regions, so we only want to count the cases where
// we are extending an existing region
Interlocked::Increment(&uoh_try_fit_segment_end_count);
if (uoh_try_fit_segment_end_count == 0)
{
uoh_try_fit_segment_end_count = 1;
uoh_try_fit_segment_end_fail_count = 0;
}
}
*commit_failed_p = FALSE;
size_t limit = 0;
bool hard_limit_short_seg_end_p = false;
Expand Down Expand Up @@ -17643,7 +17660,10 @@ BOOL gc_heap::a_fit_segment_end_p (int gen_number,
return TRUE;

found_no_fit:

if (gen_number >= loh_generation)
{
Interlocked::Increment(&uoh_try_fit_segment_end_fail_count);
}
return FALSE;
}

Expand Down Expand Up @@ -37751,6 +37771,7 @@ void gc_heap::background_mark_phase ()
if (bgc_t_join.joined())
#endif //MULTIPLE_HEAPS
{
distribute_free_regions ();
#ifdef FEATURE_USE_SOFTWARE_WRITE_WATCH_FOR_GC_HEAP
// Resetting write watch for software write watch is pretty fast, much faster than for hardware write watch. Reset
// can be done while the runtime is suspended or after the runtime is restarted, the preference was to reset while
Expand Down Expand Up @@ -43634,11 +43655,11 @@ void gc_heap::trim_youngest_desired_low_memory()
}
}

ptrdiff_t gc_heap::estimate_gen_growth (int gen_number)
ptrdiff_t gc_heap::estimate_gen_growth (int gen_number, bool for_bgc)
{
dynamic_data* dd_gen = dynamic_data_of (gen_number);
generation *gen = generation_of (gen_number);
ptrdiff_t new_allocation_gen = dd_new_allocation (dd_gen);
ptrdiff_t new_allocation_gen = for_bgc ? dd_desired_allocation (dd_gen) : dd_new_allocation (dd_gen);
ptrdiff_t free_list_space_gen = generation_free_list_space (gen);

#ifdef USE_REGIONS
Expand All @@ -43652,6 +43673,16 @@ ptrdiff_t gc_heap::estimate_gen_growth (int gen_number)
reserved_not_in_use += heap_segment_reserved (region) - heap_segment_allocated (region);
}

ptrdiff_t usable_reserved_not_in_use = reserved_not_in_use;

if (gen_number >= loh_generation)
{
// In case we were repeatedly unable to use the reserved space for partially used regions, we should
// discount the region end space as unusable. This happens rarely in SOH, but could be signficant for
// pathological LOH/POH usage (e.g. always allocates slightly more than 16M).
usable_reserved_not_in_use = (ptrdiff_t)((double)reserved_not_in_use * (1.0 - (double)uoh_try_fit_segment_end_fail_count/(double)uoh_try_fit_segment_end_count));
}

// compute how much of the allocated space is on the free list
double free_list_fraction_gen = (allocated_gen == 0) ? 0.0 : (double)(free_list_space_gen) / (double)allocated_gen;

Expand All @@ -43660,7 +43691,7 @@ ptrdiff_t gc_heap::estimate_gen_growth (int gen_number)
// e.g. if 10% of the allocated space is free, assume 10% of these 10% can get used
ptrdiff_t usable_free_space = (ptrdiff_t)(free_list_fraction_gen * free_list_space_gen);

ptrdiff_t budget_gen = new_allocation_gen - usable_free_space - reserved_not_in_use;
ptrdiff_t budget_gen = new_allocation_gen - usable_free_space - usable_reserved_not_in_use;

dprintf (REGIONS_LOG, ("h%2d gen %d budget %zd allocated: %zd, FL: %zd, reserved_not_in_use %zd budget_gen %zd",
heap_number, gen_number, new_allocation_gen, allocated_gen, free_list_space_gen, reserved_not_in_use, budget_gen));
Expand Down
7 changes: 6 additions & 1 deletion src/coreclr/gc/gcpriv.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3048,7 +3048,7 @@ class gc_heap

PER_HEAP_METHOD void trim_youngest_desired_low_memory();

PER_HEAP_METHOD ptrdiff_t estimate_gen_growth (int gen);
PER_HEAP_METHOD ptrdiff_t estimate_gen_growth (int gen, bool for_bgc = false);

PER_HEAP_METHOD void decommit_ephemeral_segment_pages();

Expand Down Expand Up @@ -4296,6 +4296,11 @@ class gc_heap
PER_HEAP_ISOLATED_FIELD_MAINTAINED_ALLOC size_t current_total_committed;
PER_HEAP_ISOLATED_FIELD_MAINTAINED_ALLOC size_t committed_by_oh[recorded_committed_bucket_counts];

// Thess are the numerator and the denominator of our estimate on how likely an existing UOH region
// can fit new allocation.
PER_HEAP_ISOLATED_FIELD_MAINTAINED_ALLOC uint32_t uoh_try_fit_segment_end_fail_count;
PER_HEAP_ISOLATED_FIELD_MAINTAINED_ALLOC uint32_t uoh_try_fit_segment_end_count;

/********************************************/
// PER_HEAP_ISOLATED_FIELD_INIT_ONLY fields //
/********************************************/
Expand Down