Reset bytes.Buffer before returning it to sync.Pool #448
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Most of bytes.Buffer in stargz-snapshotter is unbounded in terms of size and sync.Pool's Get may choose to ignore the pool. Resizing a buffer before returning to the pool may alleviate the snapshotter's memory utilization issue. golang/go#23199 has a long discussion about the issue. Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>
kzys
commented
Sep 3, 2021
| return nil | ||
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| return memW, nil | ||
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| func (dc *directoryCache) putBuffer(b *bytes.Buffer) { | ||
| b.Reset() |
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Note that calling Reset() is the safest but may not be the most efficient solution.
Go's standard library has some more sophisticated examples.
ktock
reviewed
Sep 4, 2021
| @@ -406,11 +411,10 @@ func (sf *file) ReadAt(p []byte, offset int64) (int, error) { | |||
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| // Use temporally buffer for aligning this chunk | |||
| b := sf.gr.bufPool.Get().(*bytes.Buffer) | |||
| b.Reset() | |||
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Could we remain Reset before use for safety?
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Sure, but would it have real effects? Get() returns either a new Buffer, which is safe to use according to https://cs.opensource.google/go/go/+/refs/tags/go1.17:src/bytes/buffer.go;l=449
In most cases, new(Buffer) (or just declaring a Buffer variable) is sufficient to initialize a Buffer.
or a buffer which is put by putBuffer().
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Sorry, I think you are right. Merging.
ktock
approved these changes
Sep 8, 2021
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Most of bytes.Buffer in stargz-snapshotter is unbounded in terms of
size and sync.Pool's Get may choose to ignore the pool.
Resizing a buffer before returning to the pool may alleviate the
snapshotter's memory utilization issue.
golang/go#23199 has a long discussion about
the issue.
Signed-off-by: Kazuyoshi Kato katokazu@amazon.com