On Sun, 6 Oct 2024 19:17:24 GMT, Eirik Bjørsnøs <eir...@openjdk.org> wrote:
>> Please review this PR which proposes to change the input buffer size of
>> `ZipFileInflaterInputStream` to be based on the _compressed_ size of a ZIP
>> entry instead of the _uncompressed_ size. This saves allocation since
>> buffers will no longer be oversized:
>>
>> * The `size` parameter passed to the `ZipFileInflaterInputStream`
>> constructor is passed on to the superclass `InflaterInputStream` where it
>> determines the size of the input buffer. This buffer is used to read
>> compressed data and pass it on to the `Inflater`.
>> * `ZipFile:getInputStream` currently looks at the _uncompressed_ size when
>> determining the input buffer size. It should instead use the _compressed_
>> size, since this buffer is used for compressed, not uncompressed data.
>> * The current implementation somewhat mysteriously adds 2 to the
>> uncompressed size. My guess is that this is to allow fitting a two-byte
>> DEFLATE header for empty files (where the uncompressed size is 0 and the
>> compressed size is 2).
>> * There is a check for `size <= 0`. This condition is unreachable in the
>> current code and in the PR as well, since the compressed size will always be
>> `>= 2`. I propose we remove this check.
>>
>> Performance: A benchmark which measures the cost of opening and closing
>> input streams using `ZipFile::getInputStream` shows a modest improvement of
>> ~5%, consistent with less allocation of unused buffer space.
>>
>> Testing: No tests are added in this PR. The `noreg-cleanup` label is added
>> in JBS. GHA testing is currently pending.
>
> src/java.base/share/classes/java/util/zip/ZipFile.java line 417:
>
>> 415: if (size > 65536) {
>> 416: size = 8192;
>> 417: }
>
> Not sure if this clamping makes sense? We clamp the size at 8192, but only
> when size is larger than 65536?
>
> Wondering if we should simply clamp to 8192 instead:
>
>
> Suggestion:
>
> int size = Math.clamp(CENSIZ(zsrc.cen, pos), 2, 8192);
I'm curious if it would be beneficial to increase the max clamp size to 16384
bytes similar to https://bugs.openjdk.org/browse/JDK-8299336 /
https://github.com/openjdk/jdk/pull/11783
Suggestion:
int size = Math.clamp(CENSIZ(zsrc.can, pos), 2, 16384);
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/21379#discussion_r1789364170
