fadvise64_64¶

Intro¶

fadvise64_64 - Informs the kernel of the application's advice on how it should handle the file associated with the given file descriptor

Description¶

The fadvise64_64 syscall is a system call that provides a mechanism for an application to advise the kernel of its behavior and access patterns for a file associated with a specified file descriptor. An application can provide strategies or smartly manage the page cache and associated hardware prefetch (e.g. disk read ahead) without accessing the data. fadvise64_64 provides an application with hints that allow it to better manage and group similar, potentially duplicate, data operations.

The benefit of this syscall is that, since the kernel is more aware of an application's expectations, it can efficiently manage the operations, leading to improved performance and decreased user wait time. Additionally, fadvise64_64 allows an application to inform the kernel that a range of bytes, within a file, will not be accessed again in the foreseeable future. Thus, decreasing the work the kernel has to do and, thus, conserving system resources.

On the other hand, the trade-off of using this syscall is that the kernel can no longer rely on application patterns in order to determine when to read ahead, or when to evict data from the page cache. This could lead to inefficiencies, as the application will now be responsible for data management.

Arguments¶

fd:int[K] - File descriptor associated with the given data.
offset:loff_t[K] - Offset to which the advice is required for.
len:loff_t[K] - Length of the data which it is required to be effected by the given advice.
advice:int[K] - The advice which needs to be applied on the data associated with the given file descriptor.

Available Tags¶

K - Originated from kernel-space.

Hooks¶

sys_fadvise64_64¶

Type¶

Kprobe

Purpose¶

To allow the kernel to efficiently manage the operations of the application, leading to improved performance and decreased user wait time.

Example Use Case¶

As an example, an application that streams large chunks of data from a file to an output device. Since the data will be processed and sent off in large chunks, a streaming application can advise the kernel that the data will not be accessed again, eliminating the costly pagecache eviction operation.

Issues¶

fadvise64_64 is currently unavailable on some architectures and platforms, such as MIPS. In other cases, a supported architecture or platform might be missing some features.

read - to read data from a file descriptor.
pread64 - to read from a file descriptor with a given offset.
madvise - another syscall to advise the kernel on how it should manage memory.

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.