On Wed, 19 Nov 2025 10:54:42 GMT, Harald Eilertsen <[email protected]> wrote:
>> `jdk.internal.foreign.SegmentFactories::allocateNativeInternal` assumes that
>> the underlying implementation of malloc aligns allocations on 16 byte
>> boundaries for 64 bit platforms, and 8 byte boundaries on 32 bit platforms.
>> So for any allocation where the requested alignment is less than or equal to
>> this default alignment it makes no adjustment.
>>
>> However, this assumption does not hold for all allocators. Specifically
>> jemallc, used by libc on FreeBSD will align small allocations on 8 or 4 byte
>> boundaries, respectively. This causes allocateNativeInternal to sometimes
>> return memory that is not properly aligned when the requested alignment is
>> exactly 16 bytes.
>>
>> To make sure we honour the requested alignment when it exaclty matches the
>> quantum as defined by MAX_MALLOC_ALIGN, this patch ensures that we adjust
>> the alignment also in this case.
>>
>> This should make no difference for platforms where malloc allready aligns on
>> the quantum, except for a few unnecessary trivial calculations.
>>
>> This work was sponsored by: The FreeBSD Foundation
>
> Harald Eilertsen has updated the pull request incrementally with one
> additional commit since the last revision:
>
> use suggested solution by bsdkurt
src/java.base/share/classes/jdk/internal/foreign/SegmentFactories.java line 215:
> 213: result = Utils.alignUp(allocationBase, byteAlignment);
> 214: } else {
> 215: allocationSize = (alignedSize < byteAlignment) ?
> byteAlignment : alignedSize;
This can probably use [`Math::max(long, long)`], which is an intrinsic[^1].
Suggestion:
allocationSize = Math.max(alignedSize, byteAlignment);
[^1]: For whatever reason, [`StrictMath::max(long, long)`] is the only
overload which doesn’t have `@IntrinsicCandidate`, even though it’s just a
simple call to `Math::max(long, long)`, and so gets intrisified anyway after
inlining; same with [`StrictMath::min(long, long)`] and [`Math::min(long,
long)`].
[`Math::max(long, long)`]:
https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Math.html#max%28long%2Clong%29
[`Math::min(long, long)`]:
https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Math.html#min%28long%2Clong%29
[`StrictMath::max(long, long)`]:
https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/StrictMath.html#max%28long%2Clong%29
[`StrictMath::min(long, long)`]:
https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/StrictMath.html#min%28long%2Clong%29
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/28235#discussion_r2541810615
