Adjust XML allocation pages to have the exact specified size

Previously the page size was defining the data size, and due to additional
headers (+ recently removed allocation padding) the actual allocation was a bit
bigger.

The problem is that some allocators round 2^N+k allocations to 2^N+M, which can
result in noticeable waste of space. Specifically, on 64-bit OSX allocating the
previous page size (32k+40) resulted in 32k+512 allocation, thereby wasting 472
bytes, or 1.4%.

Now we have the allocation size specified exactly and just recompute the available
data size, which can in small space savings depending on the allocator.

0 files changed, 0 insertions, 0 deletions