gh-129005: Align FileIO.readall allocation #129458
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Both now use a pre-allocated buffer of length `bufsize`, fill it using a readinto, and have matching "expand buffer" logic. On my machine this takes: `./python -m test -M8g -uall test_largefile -m test_large_read -v` from ~3.7 seconds to ~3.4 seconds
vstinner
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Jan 30, 2025
Misc/NEWS.d/next/Library/2025-01-28-21-22-44.gh-issue-129005.h57i9j.rst
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LGTM. I enabled auto-merge. |
vstinner
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srinivasreddy
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Both now use a pre-allocated buffer of length `bufsize`, fill it using a readinto(), and have matching "expand buffer" logic. On my machine this takes: `./python -m test -M8g -uall test_largefile -m test_large_read -v` from ~3.7 seconds to ~3.4 seconds.
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…9458)" (python#129572) This reverts commit f927204.
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Both
_ioand_pyionow use a pre-allocated buffer of lengthbufsize, fill it using aos.readinto/_Py_read, and have matching "expand buffer" logic.On my machine (Linux, Debug build) this takes:
./python -m test -M8g -uall test_largefile -m test_large_read -vfrom ~3.7 seconds to ~3.3 seconds_pyiostill uses 2x the memory, there are two remaining copiesbytes(result)currently copies. I'd like to either just rely on "duck typing" / bytearray is close enough to bytes, or would need to do something similar to C++ "move" semantics where the bytes could take ownership of the data buffer from the bytearray without copying... Not sure what is most Pythonic_pyio.BufferedIO._read_unlockedin the read-all case where no buffer has been allocated always doesreturn buf[:pos] + chunkwhich causes another copy. Patch for that case / "if buf is length 0, just return" coming shortly.