Readahead¶

Intro¶

Readahead - readahead preloads a file or block device into the page cache.

Description¶

The readahead() system call initiates a read from a file or block device into the page cache of the kernel. It begins at an offset in the file and reads up to count bytes. If readahead has already been performed on this file, the kernel will extend the previous read by the additional count bytes. This call allows the kernel to prefetch more data than is needed before the data is requested. Thus, the act of calling readahead allows the kernel to speed up subsequent read operations by preloading the data before it is requested by the user.

The readahead system call can be used to improve the slow-start performance of applications that read full files sequentially. By pre-loading data with readahead, the user has less wait time while the disk is being read.

Readahead does not guarantee that the data will remain in the page cache. The kernel discards quickly-referenced pages from the page cache in order to make room for other page-cache requests.

Arguments¶

fd:int[K] - The file descriptor for the file.
offset:off_t[K] - The location in the file to begin reading from.
count:size_t[K] - The amount of bytes to read.

Available Tags¶

K - Originated from kernel-space.

Hooks¶

No functions are hooked when readahead is called.

Example Use Case¶

One example use case of the readahead system call is the readahead_all() function in the Linux kernel. It is used to prefetch files in parallel to speed-up the start of an application that requires multiple files. This can significantly reduce I/O latency by allowing more data to be read in one go since the kernel can readahead to fill-up the page cache.

Issues¶

No known issues exist with the readahead system call.

madvise() - The madvise() system call can allow applications to inform the kernel about the expected usage patterns of data so that the optimal page management strategies can be implemented. It is typically used in conjunction with readahead() to optimize the performance of file reads.

This document was automatically generated by OpenAI and needs review. It might not be accurate and might contain errors. The authors of Tracee recommend that the user reads the "events.go" source file to understand the events and their arguments better.