pw::allocator::Fragmentation Struct Reference

#include <fragmentation.h>

Public Member Functions
void	AddFragment (size_t inner_size)

Public Attributes
struct {
size_t   hi = 0
size_t   lo = 0
}	sum_of_squares
	Sum-of-squares of the inner sizes of free blocks.
size_t	sum = 0
	Sum of the inner sizes of free blocks.

Detailed Description

Information that can be used to represent the fragmentation of the block allocator's memory region.

Fragmentation can be measured as 1 minus the normalized root-sum-square of the free block inner sizes, i.e.

1 - (sqrt(sum(U[i]^2)) / sum(U[i])

where U[i] is the inner size of the i-th free block.

This metric has been described by Adam Sawicki (https://asawicki.info/news_1757_a_metric_for_memory_fragmentation), and used in esp8266/Arduino (https://github.com/esp8266/Arduino/blob/master/cores/esp8266/Esp-frag.cpp), among others.

This struct provides the sum-of-squares and the sum of the inner sizes of free blocks. It is left to the caller to perform the square root and division steps, perhaps on a host, AP, or other device with better floating point support.

The sum-of-squares is stored as a pair of sizes, since it can overflow.

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The documentation for this struct was generated from the following file:

• pw_allocator/public/pw_allocator/fragmentation.h