Struct swap::page_handler::PageHandler

pub struct PageHandler<'a> {
    ctx: Mutex<PageHandleContext<'a>>,
    channel: Arc<Channel<MoveToStaging>>,
}

PageHandler manages the page states of multiple regions.

Handles multiple events derived from userfaultfd and swap out requests. All the addresses and sizes in bytes are converted to page id internally.

Fields

ctx: Mutex<PageHandleContext<'a>>

channel: Arc<Channel<MoveToStaging>>

Implementations

impl<'a> PageHandler<'a>

pub fn create( swap_file: &'a File, staging_shmem: &'a SharedMemory, address_ranges: &[Range<usize>], stating_move_context: Arc<Channel<MoveToStaging>> ) -> Result<Self>

Creates PageHandler for the given region.

If any of regions overlaps, this returns Error::RegionOverlap.

Arguments

• swap_file - The swap file.
• staging_shmem - The staging memory. It must have enough size to hold guest memory. Otherwise monitor process crashes on creating a mmap.
• address_ranges - The list of address range of the regions. the start address must align with page. the size must be multiple of pagesize.

fn find_region(regions: &mut [Region], page_idx: usize) -> Option<&mut Region>

pub fn handle_page_fault( &self, uffd: &Userfaultfd, address: usize ) -> Result<()>

Fills the faulted page with zero if the page is not initialized, with the content in the swap file if the page is swapped out.

Arguments

• uffd - the reference to the Userfaultfd for the faulting process.
• address - the address that triggered the page fault.

pub fn handle_page_remove( &self, start_addr: usize, end_addr: usize ) -> Result<()>

Clear the internal state for the pages.

When pages are removed by madvise with MADV_DONTNEED or MADV_REMOVE, userfaultfd notifies the event as UFFD_EVENT_REMOVE. This handles the remove event.

In crosvm, balloon frees the guest memory and cause UFFD_EVENT_REMOVE.

Arguments

• start_addr - the head address of the memory area to be freed.
• end_addr - the end address of the memory area to be freed. UFFD_EVENT_REMOVE tells the head address of the next memory area of the freed area. (i.e. the exact tail address of the memory area is end_addr - 1.)

pub unsafe fn move_to_staging<T>( &self, base_addr: usize, memfd: &T, base_offset: u64 ) -> Result<usize>

where T: AsRawDescriptor,

Move active pages in the memory region to the staging memory.

It only moves active contents in the guest memory to the swap file and skips empty pages (e.g. pages not touched, freed by balloon) using lseek(2) + SEEK_HOLE/DATA.

Returns the count of moved out pages.

Arguments

• base_addr - the head address of the memory region.
• memfd - the file descriptor of the memfd backing the guest memory region.
• base_offset - the offset of the memory region in the memfd.

Safety

The region must have been registered to all userfaultfd of processes which may touch the region.

The memory must be protected not to be updated while moving.

The page fault events for the region from the userfaultfd must be handled by Self::handle_page_fault().

Must call Channel::wait_complete() to wait all the copy operation complete within the memory protection period.

pub fn swap_out(&self, max_size: usize) -> Result<usize>

Write a chunk of consecutive pages in the staging memory to the swap file.

If there is no active pages in the staging memory, this returns Ok(0).

The pages in guest memory have been moved to staging memory by Self::move_to_staging().

Returns the count of swapped out pages.

Even if swap_out fails on any internal steps, it does not break the page state management and PageHandler can continue working with a little pages leaking in staging memory or swap file. The leaked pages are removed when vmm-swap is disabled and PageHandler is dropped.

Arguments

• max_size - the upper limit of the chunk size to write into the swap file at once. The chunk is splitted if it is bigger than max_size.

pub fn start_swap_in(&'a self) -> SwapInContext<'a>

Create a new SwapInContext.

pub fn start_trim(&'a self) -> TrimContext<'a>

Create a new TrimContext.

fn compute_copied_from_file_pages(&self) -> usize

Returns count of pages copied from vmm-swap file to the guest memory.

fn compute_copied_from_staging_pages(&self) -> usize

Returns count of pages copied from staging memory to the guest memory.

fn compute_zeroed_pages(&self) -> usize

Returns count of pages initialized with zero.

fn compute_redundant_pages(&self) -> usize

Returns count of pages which were already initialized on page faults.

fn compute_staging_pages(&self) -> usize

Returns count of pages present in the staging memory.

fn compute_swap_pages(&self) -> usize

Returns count of pages present in the swap files.

pub fn load_metrics(&self, metrics: &mut SwapMetrics)

Fill SwapMetrics with page handler metrics.