吴志勇:Linux VFS层热跟踪概述.pdf
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1、Linux is a registered trademark of Linus Torvalds. VFS hot tracking Development Overview Zhi Yong Wu Kernel Team IBM Linux Technology Center October 19, 2013 Agenda Background Methodology Internals Performance Status & Next References Background Problem: SSD disks has high IOPS(Input/Output Per Sec
2、ond) and low capability, while traditional disks has opposite peculiarities. Some data are highly accessed, while some are rarely. Vision: Place hot data on fast disks as far as possible. Defrag hot files as first as possible Proposal: Trace and detect hot data on the filesystem Relocate hot data to
3、 fast disks Defrag the files based on hot information How to track? Track real disk I/O access, not I/O hit in page cache Track accessed inodes and its ranges whose granularity is 1 MegaByte The key is ino inode offset range Track each read/write on I/O path, including buffered and direct mode How t
4、o find hot spots? Each hot item is stored in Inserted into rb_tree Linked to hot map list Each hot item is indexed in two ways One by ino or offset in rb_tree, used to quickly update data access frequency One by temperature in hot map array, used to quickly lookup hot spots One delayed worker is que
5、ued periodically to update the temperature of each hot item, and move it to irresponding hot map list based on its temperature. Data Structures Structure Relationship Record I/O access info Lookup hot_inode_item by its ino Check if VFS hot tracking is enabled Check if hot_inode_item has existed Crea
6、te hot_inode_item Update hot_inode_item Check if hot_range_item has existed Lookup hot_range_item by its offset Update hot_range_item Create hot_range_item Check if length is reached Start End Update hot map periodically Walk through the rb_tree of hot_inode_item Check if the end of the rb_tree of h
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