Fix GH-13071: Copying large files using mmap-able source streams may exhaust available memory and fail #13136
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…ay exhaust available memory and fail Commit 5cbe5a5 disabled chunking for all writes to streams. However, user streams have a callback where code is executed on data that is subject to the memory limit. Therefore, when using large writes or stream_copy_to_stream/copy the memory limit can easily be hit with large enough data. To solve this, we reintroduce chunking for userspace streams. Users have control over the chunk size, which is neat because they can improve the performance by setting the chunk size if that turns out to be a bottleneck. In an ideal world, we add an option so we can "ask" the stream whether it "prefers" chunked writes, similar to how we have php_stream_mmap_supported & friends. However, that cannot be done on stable branches.
bukka
reviewed
Jan 16, 2024
Okay I've added a simplified test based on the original code and it seems to pass. |
bukka
approved these changes
Jan 16, 2024
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Commit 5cbe5a5 disabled chunking for all writes to streams. However, user streams have a callback where code is executed on data that is subject to the memory limit. Therefore, when using large writes or stream_copy_to_stream/copy the memory limit can easily be hit with large enough data.
To solve this, we reintroduce chunking for userspace streams. Users have control over the chunk size, which is neat because they can improve the performance by setting the chunk size if that turns out to be a bottleneck.
In an ideal world, we add an option so we can "ask" the stream whether it "prefers" chunked writes, similar to how we have php_stream_mmap_supported & friends. However, that cannot be done on stable branches.