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fix: reduce index load memory spike #204

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fix: reduce index load memory spike #204

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63 changes: 43 additions & 20 deletions include/svs/core/allocator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,11 @@
/// @file
/// @brief Implements common large-scale allocators used by the many data structures.
///
/// Memory Population Control:
/// Setting environment variable `SVS_ENABLE_MAP_POPULATE` enables MAP_POPULATE for
/// hugepage and file-backed mappings (Linux only). By default population is disabled
/// to avoid transient RSS spikes during large index loads. Use the variable for
/// benchmarking scenarios where early page faulting is desired.

///
/// @ingroup core
Expand Down Expand Up @@ -112,6 +117,13 @@ struct HugepageAllocation {
assert(bytes != 0);
void* ptr = MAP_FAILED;
size_t sz = 0;
// Allow disabling page population via environment variable to mitigate peak RSS.
// If SVS_DISABLE_MAP_POPULATE is set to a non-empty value, MAP_POPULATE will not be
// used. Population now disabled by default; opt-in via SVS_ENABLE_MAP_POPULATE.
const bool enable_populate = (std::getenv("SVS_ENABLE_MAP_POPULATE") != nullptr);
// Heuristic: Skip attempting huge pages whose rounded allocation would exceed 2x
// requested. This avoids over-large temporary mappings when the user dataset is
// smaller.
for (auto params : hugepage_x86_options) {
// Don't fallback to huge pages if `force == true`.
if (force && params == hugepage_x86_options.back()) {
Expand All @@ -122,6 +134,11 @@ struct HugepageAllocation {
auto flags = params.mmap_flags;
sz = lib::round_up_to_multiple_of(bytes, pagesize);

if (sz > 2 * bytes) {
// Skip this page size; too much waste for transient attempt.
continue;
}

int mmap_flags = MAP_PRIVATE;
#if defined(MAP_ANONYMOUS)
mmap_flags |= MAP_ANONYMOUS;
Expand All @@ -132,7 +149,9 @@ struct HugepageAllocation {
#endif
// Add Linux-specific flags
#ifdef __linux__
mmap_flags |= MAP_POPULATE;
if (enable_populate) {
mmap_flags |= MAP_POPULATE;
}
#endif // __linux__

ptr = mmap(nullptr, sz, PROT_READ | PROT_WRITE, mmap_flags | flags, -1, 0);
Expand Down Expand Up @@ -362,8 +381,9 @@ template <typename T> class MMapPtr {
// Make the conversion from "void" to non-void "explicit" to avoid nasty unexpected
// implicit conversions.
template <typename OtherT>
requires(std::is_same_v<OtherT, T> || std::is_same_v<OtherT, void>)
MMapPtr(MMapPtr<OtherT>&& other) noexcept
requires(std::is_same_v<OtherT, T> || std::is_same_v<OtherT, void>)
MMapPtr(MMapPtr<OtherT>&& other)
noexcept
: ptr_{reinterpret_cast<T*>(other.ptr_)}
, base_{other.base_}
, size_{other.size_} {
Expand Down Expand Up @@ -517,9 +537,13 @@ class MemoryMapper {
int mmap_flags = MAP_SHARED; // Accessible from all processes
// Add Linux-specific flags
#ifdef __linux__
// Respect environment variable disabling population.
const bool enable_populate = (std::getenv("SVS_ENABLE_MAP_POPULATE") != nullptr);
mmap_flags |= MAP_NORESERVE; // Don't reserve space in DRAM for this until used
mmap_flags |= MAP_POPULATE; // Populate page table entries in the DRAM
#endif // __linux__
if (enable_populate) {
mmap_flags |= MAP_POPULATE; // Populate page table entries in the DRAM
}
#endif // __linux__

void* base = ::mmap(
nullptr, bytes.value(), mmap_permissions(permission_), mmap_flags, fd, 0
Expand All @@ -536,7 +560,9 @@ class MemoryMapper {
namespace detail {

template <typename Alloc>
concept HasValueType = requires { typename Alloc::value_type; };
concept HasValueType = requires {
typename Alloc::value_type;
};

// clang-format off
template <typename Alloc>
Expand Down Expand Up @@ -601,10 +627,9 @@ template <typename T> class AllocatorHandle {
using value_type = T;

template <detail::Allocator Impl>
explicit AllocatorHandle(Impl&& impl)
requires(!std::is_same_v<Impl, AllocatorHandle>) &&
std::is_rvalue_reference_v<Impl&&> &&
std::is_same_v<typename Impl::value_type, T>
explicit AllocatorHandle(Impl&& impl
) requires(!std::is_same_v<Impl, AllocatorHandle>) &&
std::is_rvalue_reference_v<Impl&&>&& std::is_same_v<typename Impl::value_type, T>
: impl_{new AllocatorImpl(std::move(impl))} {}

AllocatorHandle() {}
Expand All @@ -622,25 +647,23 @@ template <typename T> class AllocatorHandle {
template <typename U> friend class AllocatorHandle;

template <typename U>
AllocatorHandle(const AllocatorHandle<U>& other)
requires std::is_same_v<T, float> && (!std::is_same_v<U, T>)
AllocatorHandle(const AllocatorHandle<U>& other) requires std::is_same_v<T, float> &&
(!std::is_same_v<U, T>)
: impl_{other.impl_->rebind_float()} {}
template <typename U>
AllocatorHandle(const AllocatorHandle<U>& other)
requires std::is_same_v<T, Float16> && (!std::is_same_v<U, T>)
AllocatorHandle(const AllocatorHandle<U>& other) requires std::is_same_v<T, Float16> &&
(!std::is_same_v<U, T>)
: impl_{other.impl_->rebind_float16()} {}

template <typename U>
AllocatorHandle& operator=(const AllocatorHandle<U>& other)
requires std::is_same_v<T, float> && (!std::is_same_v<U, T>)
{
AllocatorHandle& operator=(const AllocatorHandle<U>& other
) requires std::is_same_v<T, float> &&(!std::is_same_v<U, T>) {
impl_.reset(other.impl_->rebind_float());
return *this;
}
template <typename U>
AllocatorHandle& operator=(const AllocatorHandle<U>& other)
requires std::is_same_v<T, Float16> && (!std::is_same_v<U, T>)
{
AllocatorHandle& operator=(const AllocatorHandle<U>& other
) requires std::is_same_v<T, Float16> &&(!std::is_same_v<U, T>) {
impl_.reset(other.impl_->rebind_float16());
return *this;
}
Expand Down
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