managed_shared_memory can't allocate a chunk of more than half its allocation any more

[JulesRapanga]

#include <unistd.h>
#include <iostream>
#include <boost/interprocess/managed_shared_memory.hpp>

using namespace boost::interprocess;

#define HEADSPACE (1 << 10)
const size_t SIZE = 20'000'000;

struct Header {
    managed_shared_memory::handle_t buf = {};
    unsigned size = 0;
    unsigned counter = 0;
};

int main()
{
    shared_memory_object::remove("Paper name");

    size_t size = SIZE;
    size_t paper_size = (sizeof(Header) + HEADSPACE + size);
    std::cerr << getpid() << " Making paper: total_size: " << paper_size << " req size: " << size << " HEADSPACE: " << (HEADSPACE) << std::endl;
    managed_shared_memory shm(open_or_create, "Paper name", paper_size);
    Header* h = shm.find_or_construct<Header>("Header")();
    void * buf = shm.allocate_aligned(size, 32);
    h->buf = shm.get_handle_from_address(buf);
    h->size = size;
}

Above is a roughly cut down version of some production code I'm running; for a given memory size, allocate create a managed_shared_memory of a slightly larger size, construct a Header in it, and allocate the desired size as an aligned buffer (stored in the header) . In 1.86.0 and before it successfully allocates all the memory, but in 1.87.0 it throws bad_alloc. Some investigation shows that the allocated_aligned step only succeeds if the size is <=1/2 of the desired size, and that allocating smaller chunks does allow access to most of the allocated memory (i.e. you can ask for 1/10 of size 9 times but the 10th fails).