Struct BestFit

pub struct BestFit { /* private fields */ }

An allocation strategy that returns the smallest extent that is large enough to hold the requested allocation, or the next best if no extent is big enough.

This strategy either leads to a perfect fit of a free extent to an allocation or a small amount of free space being left over, creating even smaller fragments of free space.

This tendency to create smaller fragments of free space starts to affect file fragmentation when filesystem use approaches capacity and there are nothing but small fragments of free space remaining.

Implementations

impl BestFit

pub fn allocate(&mut self, bytes: u64) -> Result<Range<u64>, FxfsError>

Tries to assign a set of contiguous bytes and returns the range, removing it from the pool of available bytes and returning it.

If insufficient contiguous space is available, the largest available range will be returned. If no bytes are available, None will be returned.

There are no special requirements on alignment of bytes but the caller is generally encouraged to align to device block size.

pub fn force_free(&mut self, range: Range<u64>) -> Result<bool, Error>

This is effectively an optimized path for “remove” followed by “free” on the same range. Returns true if this resulted in changes to overall free space.

pub fn remove(&mut self, range: Range<u64>)

Removes all free extents in the given range.

pub fn overflow_markers(&self) -> Vec<u64>

Returns the set of buckets that have overflow markers.

pub fn reset_overflow_markers(&mut self)

pub fn free(&mut self, range: Range<u64>) -> Result<(), Error>

Adds an arbitrary range of bytes to the pool of available ranges.

Note that we keep these ranges in a map keyed by their length. To bound the size of this map we only track ranges up to N blocks long (up to 2MB). Longer ranges are broken up into ranges of this size.

Trait Implementations

impl Debug for BestFit

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for BestFit

fn default() -> BestFit

Returns the “default value” for a type.