Using synchronized_pool_resource with largest_required_pool_block > 1mb does not work

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We are trying to use std::pmr:::synchronized_pool_resource with a pool block size of 16 * 1024 * 1024, but this will cause the pmr allocator to request an alignment of 4 * 1024 * 1024, resulting in an assert/error because MI_ALIGNMENT_MAX is 1024 * 1024.

mimalloc: error: aligned allocation has a maximum alignment of 1048576 (size 16777272, alignment 4194304)

Versions of mimalloc we tried: 1.6.7, 1.7.5, 2.0.3.

Is there any way to work around this without setting the largest_required_pool_block to 1024*1024? We would like pooling to work for bigger blocks than this.

Start by reproducing the issue with std::pmr::synchronized_pool_resource and largest_required_pool_block set to 16 * 1024 * 1024. Trace how the resulting 4 * 1024 * 1024 alignment reaches mimalloc, then verify that pooling works for blocks larger than 1 MiB without the reported alignment assertion, or document the supported limit and workaround.

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