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rocksdb/include/rocksdb/memory_allocator.h

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3.4 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <memory>
#include "rocksdb/customizable.h"
#include "rocksdb/status.h"
namespace ROCKSDB_NAMESPACE {
// MemoryAllocator is an interface that a client can implement to supply custom
// memory allocation and deallocation methods. See rocksdb/cache.h for more
// information.
// All methods should be thread-safe.
class MemoryAllocator : public Customizable {
public:
static const char* Type() { return "MemoryAllocator"; }
static Status CreateFromString(const ConfigOptions& options,
const std::string& value,
std::shared_ptr<MemoryAllocator>* result);
// Allocate a block of at least size. Has to be thread-safe.
virtual void* Allocate(size_t size) = 0;
// Deallocate previously allocated block. Has to be thread-safe.
virtual void Deallocate(void* p) = 0;
// Returns the memory size of the block allocated at p. The default
// implementation that just returns the original allocation_size is fine.
virtual size_t UsableSize(void* /*p*/, size_t allocation_size) const {
// default implementation just returns the allocation size
return allocation_size;
}
std::string GetId() const override { return GenerateIndividualId(); }
};
struct JemallocAllocatorOptions {
static const char* kName() { return "JemallocAllocatorOptions"; }
// Jemalloc tcache cache allocations by size class. For each size class,
// it caches between 20 (for large size classes) to 200 (for small size
// classes). To reduce tcache memory usage in case the allocator is access
// by large number of threads, we can control whether to cache an allocation
// by its size.
bool limit_tcache_size = false;
// Lower bound of allocation size to use tcache, if limit_tcache_size=true.
// When used with block cache, it is recommended to set it to block_size/4.
size_t tcache_size_lower_bound = 1024;
// Upper bound of allocation size to use tcache, if limit_tcache_size=true.
// When used with block cache, it is recommended to set it to block_size.
size_t tcache_size_upper_bound = 16 * 1024;
};
// Generate memory allocator which allocates through Jemalloc and utilize
// MADV_DONTDUMP through madvise to exclude cache items from core dump.
// Applications can use the allocator with block cache to exclude block cache
// usage from core dump.
//
// Implementation details:
// The JemallocNodumpAllocator creates a dedicated jemalloc arena, and all
// allocations of the JemallocNodumpAllocator are through the same arena.
// The memory allocator hooks memory allocation of the arena, and calls
// madvise() with MADV_DONTDUMP flag to exclude the piece of memory from
// core dump. Side benefit of using single arena would be reduction of jemalloc
// metadata for some workloads.
//
// To mitigate mutex contention for using one single arena, jemalloc tcache
// (thread-local cache) is enabled to cache unused allocations for future use.
// The tcache normally incurs 0.5M extra memory usage per-thread. The usage
// can be reduced by limiting allocation sizes to cache.
extern Status NewJemallocNodumpAllocator(
JemallocAllocatorOptions& options,
std::shared_ptr<MemoryAllocator>* memory_allocator);
} // namespace ROCKSDB_NAMESPACE