Linux kernel way to speed up memory allocation using slab cache memory management

Introduction

Prior approach problem

Kernel modules and drivers often need to allocate temporary storage for non-persistent structures and objects, such as inodes, task structures, and device structures. These objects are uniform in size and are allocated and released many times during the life of the kernel. In earlier Unix and Linux implementations, the usual mechanisms for creating and releasing these objects were the kmalloc() and kfree()kernel calls.

The primary motivation for slab allocation is that the initialization and destruction of kernel data objects can actually outweigh the cost of allocating memory for them. As object creation and deletion are widely employed by the kernel, overhead costs of initialization can result in significant performance drops.

Brief of Slab memory

Slab allocation is a memory management mechanism intended for the efficient memory allocation of kernel objects. It eliminates fragmentation caused by allocations and deallocations. The technique is used to retain allocated memory that contains a data object of a certain type for reuse upon subsequent allocations of objects of the same type. It is analogous to an object pool, but only applies to memory, not other resources.

Slab Overview

A slab is a set of one or more contiguous pages of memory set aside by the slab allocator for an individual cache. This memory is further divided into equal segments the size of the object type that the cache is managing (Refer: Below diagram).

Reference

https://en.wikipedia.org/wiki/Slab_allocation

http://www.secretmango.com/jimb/Whitepapers/slabs/slab.html

http://www.makelinux.net/books/lkd2/ch11lev1sec6