Linux 6.5 Nucleus Enhanced with New CacheStat System Call
In a significant development for the Linux 6.5 nucleus, changes have been accepted into the code base to implement the new system call “CacheStat“. This system call allows programs in the user’s space to request more detailed statistics from the page cache on the side of the nucleus.
The CacheStat system call expands the functionality of the existing system call “Mincore”, which is used to determine the presence of pages in memory. With CacheStat, more detailed statistics of the page cache can be requested, aiming to provide greater versatility. The system call provides information on various metrics, including the number of dirty pages, replaced pages, recently displaced pages, and pages marked for postponed recording (WriteBack).
The availability of detailed file statistics enables more accurate decision-making when working with input and output through VFS. Instead of relying solely on abstract algorithms, the characteristics of the specific system at a particular time can now be taken into account.
Possible applications of the CacheStat system call include:
- The query planner of database management systems can now decide whether to scan the index or directly read data from the table based on the state of the tabular index in the page cache.
- Granularity and load-dependency of page cache filling and input/output can be adjusted by considering metrics like “dirty” pages and pages marked for postponed recording (WriteBack), allowing for more efficient synchronization.
- Important memory usage information for large files/directories can be presented in a visual and convenient manner, similar to how the “DU” utility displays disk space usage.
- Diagnosing and debugging postponed entry problems affecting performance is simplified with the help of CacheStat.