Realloc slice exponentially in mfs
`registry/storage/driver/inmemory/driver_test.go` times out after ~10min. The slow test is `testsuites.go:TestWriteReadLargeStreams()` which writes a 5GB file. Root cause is inefficient slice reallocation algorithm. The slice holding file bytes grows only 32K on each allocation. To fix it, this PR grows slice exponentially. Signed-off-by: Wei Meng <wemeng@microsoft.com>pull/3686/head
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@ -290,18 +290,28 @@ func (f *file) ReadAt(p []byte, offset int64) (n int, err error) {
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return copy(p, f.data[offset:]), nil
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}
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// reallocExponent is the exponent used to realloc a slice. The value roughly
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// follows the behavior of Go built-in append function.
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const reallocExponent = 1.25
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func (f *file) WriteAt(p []byte, offset int64) (n int, err error) {
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off := int(offset)
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if cap(f.data) < off+len(p) {
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data := make([]byte, len(f.data), off+len(p))
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newLen := offset + int64(len(p))
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if int64(cap(f.data)) < newLen {
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// Grow slice exponentially to ensure amortized linear time complexity
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// of reallocation
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newCap := int64(float64(cap(f.data)) * reallocExponent)
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if newCap < newLen {
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newCap = newLen
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}
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data := make([]byte, len(f.data), newCap)
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copy(data, f.data)
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f.data = data
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}
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f.mod = time.Now()
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f.data = f.data[:off+len(p)]
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f.data = f.data[:newLen]
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return copy(f.data[off:off+len(p)], p), nil
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return copy(f.data[offset:newLen], p), nil
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}
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func (f *file) String() string {
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