slabmalloc 0.11.0

use env_logger;
use rand;
use std::alloc;
use std::alloc::Layout;
use std::collections::HashSet;
use std::mem::{size_of, transmute};
use std::prelude::v1::*;

use crate::*;
use test::Bencher;

/// A simple page allocator based on GlobalAlloc (for testing purposes).
struct Pager {
    base_pages: HashSet<*mut u8>, // probably should be hash-tables
    large_pages: HashSet<*mut u8>,
}

unsafe impl Send for Pager {}
unsafe impl Sync for Pager {}

impl Pager {
    pub fn new() -> Pager {
        Pager {
            base_pages: HashSet::with_capacity(1024),
            large_pages: HashSet::with_capacity(128),
        }
    }
}

impl Pager {
    pub fn currently_allocated(&self) -> usize {
        self.base_pages.len() + self.large_pages.len()
    }

    fn alloc_page(&mut self, page_size: usize) -> Option<*mut u8> {
        let r =
            unsafe { std::alloc::alloc(Layout::from_size_align(page_size, page_size).unwrap()) };

        if !r.is_null() {
            match page_size {
                OBJECT_PAGE_SIZE => self.base_pages.insert(r),
                LARGE_OBJECT_PAGE_SIZE => self.large_pages.insert(r),
                _ => unreachable!("invalid page-size supplied"),
            };
            Some(r)
        } else {
            None
        }
    }

    fn dealloc_page(&mut self, ptr: *mut u8, page_size: usize) {
        let layout = match page_size {
            OBJECT_PAGE_SIZE => {
                assert!(
                    self.base_pages.contains(&ptr),
                    "Trying to deallocate invalid base-page"
                );
                self.base_pages.remove(&ptr);
                Layout::from_size_align(OBJECT_PAGE_SIZE, OBJECT_PAGE_SIZE).unwrap()
            }
            LARGE_OBJECT_PAGE_SIZE => {
                assert!(
                    self.large_pages.contains(&ptr),
                    "Trying to deallocate invalid large-page"
                );
                self.large_pages.remove(&ptr);
                Layout::from_size_align(LARGE_OBJECT_PAGE_SIZE, LARGE_OBJECT_PAGE_SIZE).unwrap()
            }
            _ => unreachable!("invalid page-size supplied"),
        };

        unsafe { std::alloc::dealloc(ptr, layout) };
    }
}

trait PageProvider<'a>: Send {
    fn allocate_page(&mut self) -> Option<&'a mut ObjectPage<'a>>;
    fn release_page(&mut self, page: &'a mut ObjectPage<'a>);

    fn allocate_large_page(&mut self) -> Option<&'a mut LargeObjectPage<'a>>;
    fn release_large_page(&mut self, page: &'a mut LargeObjectPage<'a>);
}

impl<'a> PageProvider<'a> for Pager {
    /// Allocates a new ObjectPage from the system.
    ///
    /// Uses `mmap` to map a page and casts it to a ObjectPage.
    fn allocate_page(&mut self) -> Option<&'a mut ObjectPage<'a>> {
        self.alloc_page(OBJECT_PAGE_SIZE)
            .map(|r| unsafe { transmute(r as usize) })
    }

    /// Release a ObjectPage back to the system.slab_page
    ///
    /// Uses `munmap` to release the page back to the OS.
    fn release_page(&mut self, p: &'a mut ObjectPage<'a>) {
        self.dealloc_page(p as *const ObjectPage as *mut u8, OBJECT_PAGE_SIZE);
    }

    /// Allocates a new ObjectPage from the system.
    ///
    /// Uses `mmap` to map a page and casts it to a ObjectPage.
    fn allocate_large_page(&mut self) -> Option<&'a mut LargeObjectPage<'a>> {
        self.alloc_page(LARGE_OBJECT_PAGE_SIZE)
            .map(|r| unsafe { transmute(r as usize) })
    }

    /// Release a LargeObjectPage back to the system.slab_page
    ///
    /// Uses `munmap` to release the page back to the OS.
    fn release_large_page(&mut self, p: &'a mut LargeObjectPage<'a>) {
        self.dealloc_page(
            p as *const LargeObjectPage as *mut u8,
            LARGE_OBJECT_PAGE_SIZE,
        );
    }
}

#[test]
fn check_size() {
    assert_eq!(
        OBJECT_PAGE_SIZE as usize,
        size_of::<ObjectPage>(),
        "ObjectPage should be exactly the size of a single page."
    );

    assert_eq!(
        LARGE_OBJECT_PAGE_SIZE as usize,
        size_of::<LargeObjectPage>(),
        "LargeObjectPage should be exactly the size of a large-page."
    );
}

#[test]
fn test_mmap_allocator() {
    let mut mmap = Pager::new();

    match mmap.allocate_page() {
        Some(sp) => {
            sp.bitfield.initialize(8, OBJECT_PAGE_SIZE - 80);
            assert!(!sp.is_full(), "Got empty slab");
            assert!(sp.is_empty(6 * 64), "Got empty slab");
            mmap.release_page(sp)
        }
        None => panic!("failed to allocate ObjectPage"),
    }

    match mmap.allocate_large_page() {
        Some(lp) => {
            lp.bitfield.initialize(8, LARGE_OBJECT_PAGE_SIZE - 80);
            assert!(!lp.is_full(), "Got empty slab");
            assert!(lp.is_empty(8 * 64), "Got empty slab");
            mmap.release_large_page(lp)
        }
        None => panic!("failed to allocate LargeObjectPage"),
    }
}

macro_rules! test_sc_allocation {
    ($test:ident, $size:expr, $alignment:expr, $allocations:expr, $type:ty) => {
        #[test]
        fn $test() {
            let _ = env_logger::try_init();
            let mut mmap = Pager::new();
            {
                let mut sa: SCAllocator<$type> = SCAllocator::new($size);
                let alignment = $alignment;

                let mut objects: Vec<NonNull<u8>> = Vec::new();
                let mut vec: Vec<(usize, &mut [usize; $size / 8])> = Vec::new();
                let layout = Layout::from_size_align($size, alignment).unwrap();

                for _ in 0..$allocations {
                    loop {
                        match sa.allocate(layout) {
                            // Allocation was successful
                            Ok(nptr) => {
                                unsafe {
                                    vec.push((rand::random::<usize>(), transmute(nptr.as_ptr())))
                                };
                                objects.push(nptr);
                                break;
                            }
                            // Couldn't allocate need to refill first
                            Err(AllocationError::OutOfMemory) => {
                                let page = mmap.allocate_page().unwrap();
                                unsafe {
                                    sa.refill(page);
                                }
                            }
                            // Unexpected errors
                            Err(AllocationError::InvalidLayout) => unreachable!("Unexpected error"),
                        }
                    }
                }

                // Write the objects with a random pattern
                for item in vec.iter_mut() {
                    let (pattern, ref mut obj) = *item;
                    assert!(obj.len() == $size / 8);
                    for i in 0..obj.len() {
                        obj[i] = pattern;
                    }
                }

                for item in vec.iter() {
                    let (pattern, ref obj) = *item;
                    for i in 0..obj.len() {
                        assert_eq!(
                            obj[i], pattern,
                            "No two allocations point to the same memory."
                        );
                    }
                }

                // Make sure we can correctly deallocate:
                let pages_allocated = sa.slabs.elements;

                // Deallocate all the objects
                for item in objects.iter_mut() {
                    sa.deallocate(*item, layout).expect("Can't deallocate");
                }

                objects.clear();
                sa.check_page_assignments();

                // then allocate everything again,
                for _ in 0..$allocations {
                    loop {
                        match sa.allocate(layout) {
                            // Allocation was successful
                            Ok(nptr) => {
                                unsafe {
                                    vec.push((rand::random::<usize>(), transmute(nptr.as_ptr())))
                                };
                                objects.push(nptr);
                                break;
                            }
                            // Couldn't allocate need to refill first
                            Err(AllocationError::OutOfMemory) => {
                                let page = mmap.allocate_page().unwrap();
                                unsafe {
                                    sa.refill(page);
                                }
                            }
                            // Unexpected errors
                            Err(AllocationError::InvalidLayout) => unreachable!("Unexpected error"),
                        }
                    }
                }

                // and make sure we do not request more pages than what we had previously
                // println!("{} {}", pages_allocated, sa.slabs.elements);
                assert_eq!(
                    pages_allocated, sa.slabs.elements,
                    "Did not use more memory for 2nd allocation run."
                );

                // Deallocate everything once more
                for item in objects.iter_mut() {
                    sa.deallocate(*item, layout).expect("Can't deallocate");
                }

                // Drain the slab-allocator and give unused pages back to the OS
                sa.try_reclaim_pages(usize::MAX, &mut |p: *mut ObjectPage| unsafe {
                    mmap.release_page(&mut *p)
                });
            }

            // Check that we released everything to our page allocator:
            assert_eq!(
                mmap.currently_allocated(),
                0,
                "Released all pages to the underlying memory manager."
            );
        }
    };
}

test_sc_allocation!(op_512_size8_alignment1, 8, 1, 512, ObjectPage);
test_sc_allocation!(op_4096_size8_alignment8, 8, 8, 4096, ObjectPage);
test_sc_allocation!(op_500_size8_alignment64, 8, 64, 500, ObjectPage);
test_sc_allocation!(op_4096_size12_alignment1, 12, 1, 4096, ObjectPage);
test_sc_allocation!(op_4096_size13_alignment1, 13, 1, 4096, ObjectPage);
test_sc_allocation!(op_2000_size14_alignment1, 14, 1, 2000, ObjectPage);
test_sc_allocation!(op_4096_size15_alignment1, 15, 1, 4096, ObjectPage);
test_sc_allocation!(op_8000_size16_alignment1, 16, 1, 8000, ObjectPage);
test_sc_allocation!(op_1024_size24_alignment1, 24, 1, 1024, ObjectPage);
test_sc_allocation!(op_3090_size32_alignment1, 32, 1, 3090, ObjectPage);
test_sc_allocation!(op_4096_size64_alignment1, 64, 1, 4096, ObjectPage);
test_sc_allocation!(op_1000_size512_alignment1, 512, 1, 1000, ObjectPage);
test_sc_allocation!(op_4096_size1024_alignment1, 1024, 1, 4096, ObjectPage);
test_sc_allocation!(op_10_size2048_alignment1, 2048, 1, 10, ObjectPage);
test_sc_allocation!(op_10000_size512_alignment1, 512, 1, 10000, ObjectPage);

macro_rules! lop_allocation {
    ($test:ident, $size:expr, $alignment:expr, $allocations:expr, $type:ty) => {
        #[test]
        fn $test() {
            let _ = env_logger::try_init();
            let mut mmap = Pager::new();
            {
                let mut sa: SCAllocator<$type> = SCAllocator::new($size);
                let alignment = $alignment;

                let mut objects: Vec<NonNull<u8>> = Vec::new();
                let mut vec: Vec<(usize, &mut [usize; $size / 8])> = Vec::new();
                let layout = Layout::from_size_align($size, alignment).unwrap();

                for _ in 0..$allocations {
                    loop {
                        match sa.allocate(layout) {
                            // Allocation was successful
                            Ok(nptr) => {
                                unsafe {
                                    vec.push((rand::random::<usize>(), transmute(nptr.as_ptr())))
                                };
                                objects.push(nptr);
                                break;
                            }
                            // Couldn't allocate need to refill first
                            Err(AllocationError::OutOfMemory) => {
                                let page = mmap.allocate_large_page().unwrap();
                                unsafe {
                                    sa.refill(page);
                                }
                            }
                            // Unexpected errors
                            Err(AllocationError::InvalidLayout) => unreachable!("Unexpected error"),
                        }
                    }
                }

                // Write the objects with a random pattern
                for item in vec.iter_mut() {
                    let (pattern, ref mut obj) = *item;
                    assert!(obj.len() == $size / 8);
                    for i in 0..obj.len() {
                        obj[i] = pattern;
                    }
                }

                for item in vec.iter() {
                    let (pattern, ref obj) = *item;
                    for i in 0..obj.len() {
                        assert_eq!(
                            obj[i], pattern,
                            "No two allocations point to the same memory."
                        );
                    }
                }

                // Make sure we can correctly deallocate:
                let pages_allocated = sa.slabs.elements;

                // Deallocate all the objects
                for item in objects.iter_mut() {
                    sa.deallocate(*item, layout).expect("Can't deallocate");
                }

                objects.clear();
                sa.check_page_assignments();

                // then allocate everything again,
                for _ in 0..$allocations {
                    loop {
                        match sa.allocate(layout) {
                            // Allocation was successful
                            Ok(nptr) => {
                                unsafe {
                                    vec.push((rand::random::<usize>(), transmute(nptr.as_ptr())))
                                };
                                objects.push(nptr);
                                break;
                            }
                            // Couldn't allocate need to refill first
                            Err(AllocationError::OutOfMemory) => {
                                let page = mmap.allocate_large_page().unwrap();
                                unsafe {
                                    sa.refill(page);
                                }
                            }
                            // Unexpected errors
                            Err(AllocationError::InvalidLayout) => unreachable!("Unexpected error"),
                        }
                    }
                }

                // and make sure we do not request more pages than what we had previously
                // println!("{} {}", pages_allocated, sa.slabs.elements);
                assert_eq!(
                    pages_allocated, sa.slabs.elements,
                    "Did not use more memory for 2nd allocation run."
                );

                // Deallocate everything once more
                for item in objects.iter_mut() {
                    sa.deallocate(*item, layout).expect("Can't deallocate");
                }

                // Drain the slab-allocator and give unused pages back to the OS
                sa.check_page_assignments();
                while let Some(page) = sa.empty_slabs.pop() {
                    mmap.release_large_page(page);
                }
            }

            // Check that we released everything to our page allocator:
            assert_eq!(
                mmap.currently_allocated(),
                0,
                "Released all pages to the underlying memory manager."
            );
        }
    };
}

lop_allocation!(lop_4096_3, 8, 1, 1024, LargeObjectPage);
lop_allocation!(lop_4096_12, 4096, 4096, 2048, LargeObjectPage);
lop_allocation!(lop_4096_13, 1 << 13, 4096, 4096, LargeObjectPage);
lop_allocation!(lop_4096_14, 1 << 14, 4096, 4096, LargeObjectPage);
lop_allocation!(lop_4096_15, 1 << 15, 4096, 4096, LargeObjectPage);
lop_allocation!(lop_4096_16, 1 << 16, 4096, 4096, LargeObjectPage);
lop_allocation!(lop_4096_17, 1 << 17, 4096, 4096, LargeObjectPage);

#[test]
#[should_panic]
fn invalid_alignment() {
    let _layout = Layout::from_size_align(10, 3).unwrap();
}

#[test]
fn test_readme() -> Result<(), AllocationError> {
    let object_size = 12;
    let alignment = 4;
    let layout = Layout::from_size_align(object_size, alignment).unwrap();

    // We need something that can provide backing memory
    // (4 KiB and 2 MiB pages) to our ZoneAllocator
    // (see tests.rs for a dummy implementation).
    let mut pager = Pager::new();
    let page = pager.allocate_page().expect("Can't allocate a page");

    let mut zone: ZoneAllocator = Default::default();
    // Prematurely fill the ZoneAllocator with memory.
    // Alternatively, the allocate call would return an
    // error which we can capture to refill on-demand.
    unsafe { zone.refill(layout, page)? };

    let allocated = zone.allocate(layout)?;
    zone.deallocate(allocated, layout)?;

    Ok(())
}

#[test]
fn test_readme2() -> Result<(), AllocationError> {
    let object_size = 10;
    let alignment = 8;
    let layout = Layout::from_size_align(object_size, alignment).unwrap();

    // We need something that can provide backing memory
    // (4 KiB and 2 MiB pages) to our ZoneAllocator
    // (see tests.rs for a dummy implementation).
    let mut pager = Pager::new();
    let page = pager.allocate_page().expect("Can't allocate a page");

    let mut sa: SCAllocator<ObjectPage> = SCAllocator::new(object_size);
    // Prematurely fill the SCAllocator with memory.
    // Alternatively, the allocate call would return an
    // error which we can capture to refill on-demand.
    unsafe { sa.refill(page) };

    sa.allocate(layout)?;
    Ok(())
}

#[test]
fn test_bug1() -> Result<(), AllocationError> {
    let _ = env_logger::try_init();

    let mut mmap = Pager::new();
    let page = mmap.allocate_page();

    let mut sa: SCAllocator<ObjectPage> = SCAllocator::new(8);
    unsafe {
        sa.refill(page.unwrap());
    }

    let ptr1 = sa.allocate(Layout::from_size_align(1, 1).unwrap())?;
    let ptr2 = sa.allocate(Layout::from_size_align(2, 1).unwrap())?;
    sa.deallocate(ptr1, Layout::from_size_align(1, 1).unwrap())?;
    let _ptr3 = sa.allocate(Layout::from_size_align(4, 1).unwrap())?;
    sa.deallocate(ptr2, Layout::from_size_align(2, 1).unwrap())
}

#[bench]
fn slabmalloc_allocate_deallocate(b: &mut Bencher) {
    let _ = env_logger::try_init();

    let mut mmap = Pager::new();
    let mut sa: SCAllocator<ObjectPage> = SCAllocator::new(8);
    let layout = Layout::from_size_align(8, 1).unwrap();

    let page = mmap.allocate_page();
    unsafe {
        sa.refill(page.unwrap());
    }

    let ptr = sa.allocate(layout).expect("Can't allocate");
    test::black_box(ptr);
    b.iter(|| {
        let ptr = sa.allocate(layout).expect("Can't allocate");
        test::black_box(ptr);
        sa.deallocate(ptr, layout).expect("Can't deallocate");
    });
}

#[bench]
fn slabmalloc_allocate_deallocate_big(b: &mut Bencher) {
    let _ = env_logger::try_init();

    let mut mmap = Pager::new();
    let mut sa: SCAllocator<ObjectPage> = SCAllocator::new(512);

    let page = mmap.allocate_page();
    unsafe {
        sa.refill(page.unwrap());
    }

    let layout = Layout::from_size_align(512, 1).unwrap();
    let ptr = sa.allocate(layout).expect("Can't allocate");
    test::black_box(ptr);

    b.iter(|| {
        let ptr = sa.allocate(layout).expect("Can't allocate");
        test::black_box(ptr);
        sa.deallocate(ptr, layout).expect("Can't deallocate");
    });
}

#[bench]
fn jemalloc_allocate_deallocate(b: &mut Bencher) {
    let layout = Layout::from_size_align(8, 1).unwrap();
    let ptr = unsafe { alloc::alloc(layout) };
    test::black_box(ptr);

    b.iter(|| unsafe {
        let ptr = alloc::alloc(layout);
        test::black_box(ptr);
        alloc::dealloc(ptr, layout);
    });
}

#[bench]
fn jemalloc_allocate_deallocate_big(b: &mut Bencher) {
    let layout = Layout::from_size_align(512, 1).unwrap();
    let ptr = unsafe { alloc::alloc(layout) };
    test::black_box(ptr);

    b.iter(|| unsafe {
        let ptr = alloc::alloc(layout);
        test::black_box(ptr);
        alloc::dealloc(ptr, layout);
    });
}

#[test]
pub fn check_first_fit() {
    let op: ObjectPage = Default::default();
    let layout = Layout::from_size_align(8, 8).unwrap();
    println!("{:?}", op.first_fit(layout));
}

#[test]
fn list_pop() {
    let mut op1: ObjectPage = Default::default();
    let op1_ptr = &op1 as *const ObjectPage<'_>;
    let mut op2: ObjectPage = Default::default();
    let op2_ptr = &op2 as *const ObjectPage<'_>;
    let mut op3: ObjectPage = Default::default();
    let op3_ptr = &op3 as *const ObjectPage<'_>;
    let mut op4: ObjectPage = Default::default();
    let op4_ptr = &op4 as *const ObjectPage<'_>;

    let mut list: PageList<ObjectPage> = PageList::new();
    list.insert_front(&mut op1);
    list.insert_front(&mut op2);
    list.insert_front(&mut op3);

    assert!(list.contains(op1_ptr));
    assert!(list.contains(op2_ptr));
    assert!(list.contains(op3_ptr));
    assert!(!list.contains(op4_ptr));

    let popped = list.pop();
    assert_eq!(popped.unwrap() as *const ObjectPage, op3_ptr);
    assert!(!list.contains(op3_ptr));

    let popped = list.pop();
    assert_eq!(popped.unwrap() as *const ObjectPage, op2_ptr);
    assert!(!list.contains(op2_ptr));

    list.insert_front(&mut op4);
    assert!(list.contains(op4_ptr));
    let popped = list.pop();
    assert_eq!(popped.unwrap() as *const ObjectPage, op4_ptr);
    assert!(!list.contains(op4_ptr));

    let popped = list.pop();
    assert_eq!(popped.unwrap() as *const ObjectPage, op1_ptr);
    assert!(!list.contains(op1_ptr));

    let popped = list.pop();
    assert!(popped.is_none());

    assert!(!list.contains(op1_ptr));
    assert!(!list.contains(op2_ptr));
    assert!(!list.contains(op3_ptr));
    assert!(!list.contains(op4_ptr));
}

#[test]
pub fn iter_empty_list() {
    let mut new_head1: ObjectPage = Default::default();
    let mut l = PageList::new();
    l.insert_front(&mut new_head1);
    for _p in l.iter_mut() {}
}

#[test]
pub fn check_is_full_8() {
    let _r = env_logger::try_init();
    let layout = Layout::from_size_align(8, 1).unwrap();

    let mut page: ObjectPage = Default::default();
    page.bitfield.initialize(8, OBJECT_PAGE_SIZE - 80);
    let obj_per_page = core::cmp::min((OBJECT_PAGE_SIZE - 80) / 8, 8 * 64);

    let mut allocs = 0;
    loop {
        if page.allocate(layout).is_null() {
            break;
        }
        allocs += 1;

        if allocs < obj_per_page {
            assert!(
                !page.is_full(),
                "Page mistakenly considered full after {} allocs",
                allocs
            );
            assert!(!page.is_empty(obj_per_page));
        }
    }

    assert_eq!(allocs, obj_per_page, "Can use all bitmap space");
    assert!(page.is_full());
}

// Test for bug that reports pages not as full when
// the entire bitfield wasn't allocated.
#[test]
pub fn check_is_full_512() {
    let _r = env_logger::try_init();
    let mut page: ObjectPage = Default::default();
    page.bitfield.initialize(512, OBJECT_PAGE_SIZE - 80);
    let layout = Layout::from_size_align(512, 1).unwrap();
    let obj_per_page = core::cmp::min((OBJECT_PAGE_SIZE - 80) / 512, 6 * 64);

    let mut allocs = 0;
    loop {
        if page.allocate(layout).is_null() {
            break;
        }

        allocs += 1;

        if allocs < (OBJECT_PAGE_SIZE - 80) / 512 {
            assert!(!page.is_full());
            assert!(!page.is_empty(obj_per_page));
        }
    }
    assert!(page.is_full());
}

#[test]
pub fn issue_9() -> Result<(), AllocationError> {
    let mut pager = Pager::new();
    let mut zone: ZoneAllocator = Default::default();

    // size: 256 align: 1 | my pager gets called
    let l1 = Layout::from_size_align(256, 1).unwrap();
    assert!(zone.allocate(l1).is_err(), "my pager gets called");
    let page = pager.allocate_page().expect("Can't allocate a page");
    unsafe { zone.refill(l1, page)? };
    let p1 = zone.allocate(l1)?;

    // size: 48 align: 8 | my pager gets called
    let l2 = Layout::from_size_align(48, 8).unwrap();
    assert!(zone.allocate(l2).is_err(), "my pager gets called");
    let page = pager.allocate_page().expect("Can't allocate a page");
    unsafe { zone.refill(l2, page)? };
    let p2 = zone.allocate(l2)?;
    assert_eq!(p2.as_ptr() as usize % l2.align(), 0);
    assert_ne!(p2, p1);

    // size: 6 align: 1 | my pager gets called and returns the properly aligned address X
    let l3 = Layout::from_size_align(6, 1).unwrap();
    assert!(
        zone.allocate(l3).is_err(),
        "my pager gets called and returns the properly aligned address X"
    );
    let page = pager.allocate_page().expect("Can't allocate a page");
    unsafe { zone.refill(l3, page)? };
    let p3 = zone.allocate(l3)?;
    assert_eq!(p3.as_ptr() as usize % l3.align(), 0);
    assert_ne!(p3, p2);
    assert_ne!(p3, p1);

    //size: 8 align: 1 | my pager doesn't get called
    let l4 = Layout::from_size_align(8, 1).unwrap();
    // my pager doesn't get called
    let p4 = zone.allocate(l4)?;
    assert_eq!(p4.as_ptr() as usize % l4.align(), 0);
    assert_ne!(p4, p3);
    assert_ne!(p4, p2);
    assert_ne!(p4, p1);

    // size: 16 align: 1 | my pager gets called
    let l5 = Layout::from_size_align(16, 1).unwrap();
    assert!(zone.allocate(l5).is_err(), "my pager gets called");
    let page = pager.allocate_page().expect("Can't allocate a page");
    unsafe { zone.refill(l5, page)? };
    let p5 = zone.allocate(l5)?;
    assert_eq!(p5.as_ptr() as usize % l5.align(), 0);
    assert_ne!(p5, p1);
    assert_ne!(p5, p2);
    assert_ne!(p5, p3);
    assert_ne!(p5, p4);

    Ok(())
}