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This commit adds a breakdown of cgo memory usage in Pebble. This will show up as part of the periodic LSM metrics dump in the logs.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,60 +1,63 @@ | ||
| // Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use | ||
| // Copyright 2024 The LevelDB-Go and Pebble Authors. All rights reserved. Use | ||
| // of this source code is governed by a BSD-style license that can be found in | ||
| // the LICENSE file. | ||
|
|
||
| package manual | ||
|
|
||
| // #include <stdlib.h> | ||
| import "C" | ||
| import "unsafe" | ||
| import ( | ||
| "fmt" | ||
| "sync/atomic" | ||
|
|
||
| // The go:linkname directives provides backdoor access to private functions in | ||
| // the runtime. Below we're accessing the throw function. | ||
| "github.com/cockroachdb/pebble/internal/invariants" | ||
| ) | ||
|
|
||
| //go:linkname throw runtime.throw | ||
| func throw(s string) | ||
| // Purpose identifies the use-case for an allocation. | ||
| type Purpose uint8 | ||
|
|
||
| // TODO(peter): Rather than relying an C malloc/free, we could fork the Go | ||
| // runtime page allocator and allocate large chunks of memory using mmap or | ||
| // similar. | ||
| const ( | ||
| _ Purpose = iota | ||
|
|
||
| // New allocates a slice of size n. The returned slice is from manually managed | ||
| // memory and MUST be released by calling Free. Failure to do so will result in | ||
| // a memory leak. | ||
| func New(n int) []byte { | ||
| if n == 0 { | ||
| return make([]byte, 0) | ||
| } | ||
| // We need to be conscious of the Cgo pointer passing rules: | ||
| // | ||
| // https://golang.org/cmd/cgo/#hdr-Passing_pointers | ||
| // | ||
| // ... | ||
| // Note: the current implementation has a bug. While Go code is permitted | ||
| // to write nil or a C pointer (but not a Go pointer) to C memory, the | ||
| // current implementation may sometimes cause a runtime error if the | ||
| // contents of the C memory appear to be a Go pointer. Therefore, avoid | ||
| // passing uninitialized C memory to Go code if the Go code is going to | ||
| // store pointer values in it. Zero out the memory in C before passing it | ||
| // to Go. | ||
| ptr := C.calloc(C.size_t(n), 1) | ||
| if ptr == nil { | ||
| // NB: throw is like panic, except it guarantees the process will be | ||
| // terminated. The call below is exactly what the Go runtime invokes when | ||
| // it cannot allocate memory. | ||
| throw("out of memory") | ||
| BlockCacheMap | ||
| BlockCacheEntry | ||
| BlockCacheData | ||
| MemTable | ||
|
|
||
| NumPurposes | ||
| ) | ||
|
|
||
| // Metrics contains memory statistics by purpose. | ||
| type Metrics [NumPurposes]struct { | ||
| // InUseBytes is the total number of bytes currently allocated. This is just | ||
| // the sum of the lengths of the allocations and does not include any overhead | ||
| // or fragmentation. | ||
| InUseBytes uint64 | ||
| } | ||
|
|
||
| var counters [NumPurposes]struct { | ||
| InUseBytes atomic.Int64 | ||
| // Pad to separate counters into cache lines. This reduces the overhead when | ||
| // multiple purposes are used frequently. We assume 64 byte cache line size | ||
| // which is the case for ARM64 servers and AMD64. | ||
| _ [7]uint64 | ||
| } | ||
|
|
||
| func recordAlloc(purpose Purpose, n int) { | ||
| counters[purpose].InUseBytes.Add(int64(n)) | ||
| } | ||
|
|
||
| func recordFree(purpose Purpose, n int) { | ||
| newVal := counters[purpose].InUseBytes.Add(-int64(n)) | ||
| if invariants.Enabled && newVal < 0 { | ||
| panic(fmt.Sprintf("negative counter value %d", newVal)) | ||
| } | ||
| // Interpret the C pointer as a pointer to a Go array, then slice. | ||
| return (*[MaxArrayLen]byte)(unsafe.Pointer(ptr))[:n:n] | ||
| } | ||
|
|
||
| // Free frees the specified slice. | ||
| func Free(b []byte) { | ||
| if cap(b) != 0 { | ||
| if len(b) == 0 { | ||
| b = b[:cap(b)] | ||
| } | ||
| ptr := unsafe.Pointer(&b[0]) | ||
| C.free(ptr) | ||
| // GetMetrics returns manual memory usage statistics. | ||
| func GetMetrics() Metrics { | ||
| var res Metrics | ||
| for i := range res { | ||
| // We load the freed count first to avoid a negative value, since we don't load both counters atomically. | ||
| res[i].InUseBytes = uint64(counters[i].InUseBytes.Load()) | ||
| } | ||
| return res | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,63 @@ | ||
| // Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use | ||
| // of this source code is governed by a BSD-style license that can be found in | ||
| // the LICENSE file. | ||
|
|
||
| package manual | ||
|
|
||
| // #include <stdlib.h> | ||
| import "C" | ||
| import "unsafe" | ||
|
|
||
| // The go:linkname directives provides backdoor access to private functions in | ||
| // the runtime. Below we're accessing the throw function. | ||
|
|
||
| //go:linkname throw runtime.throw | ||
| func throw(s string) | ||
|
|
||
| // TODO(peter): Rather than relying an C malloc/free, we could fork the Go | ||
| // runtime page allocator and allocate large chunks of memory using mmap or | ||
| // similar. | ||
|
|
||
| // New allocates a slice of size n. The returned slice is from manually managed | ||
| // memory and MUST be released by calling Free. Failure to do so will result in | ||
| // a memory leak. | ||
| func New(purpose Purpose, n int) []byte { | ||
| if n == 0 { | ||
| return make([]byte, 0) | ||
| } | ||
| recordAlloc(purpose, n) | ||
| // We need to be conscious of the Cgo pointer passing rules: | ||
| // | ||
| // https://golang.org/cmd/cgo/#hdr-Passing_pointers | ||
| // | ||
| // ... | ||
| // Note: the current implementation has a bug. While Go code is permitted | ||
| // to write nil or a C pointer (but not a Go pointer) to C memory, the | ||
| // current implementation may sometimes cause a runtime error if the | ||
| // contents of the C memory appear to be a Go pointer. Therefore, avoid | ||
| // passing uninitialized C memory to Go code if the Go code is going to | ||
| // store pointer values in it. Zero out the memory in C before passing it | ||
| // to Go. | ||
| ptr := C.calloc(C.size_t(n), 1) | ||
| if ptr == nil { | ||
| // NB: throw is like panic, except it guarantees the process will be | ||
| // terminated. The call below is exactly what the Go runtime invokes when | ||
| // it cannot allocate memory. | ||
| throw("out of memory") | ||
| } | ||
| // Interpret the C pointer as a pointer to a Go array, then slice. | ||
| return (*[MaxArrayLen]byte)(unsafe.Pointer(ptr))[:n:n] | ||
| } | ||
|
|
||
| // Free frees the specified slice. It has to be exactly the slice that was | ||
| // returned by New. | ||
| func Free(purpose Purpose, b []byte) { | ||
| if cap(b) != 0 { | ||
| recordFree(purpose, cap(b)) | ||
| if len(b) == 0 { | ||
| b = b[:cap(b)] | ||
| } | ||
| ptr := unsafe.Pointer(&b[0]) | ||
| C.free(ptr) | ||
| } | ||
| } |
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