The current read-ahead logic uses an inflexible algorithm with 128KB
VM_MAX_READAHEAD. Less memory leads to thrashing, more memory helps no
throughput. The new logic is simply safer and faster. It makes sure
every single read-ahead request is safe for the current load. Memory
tight systems are expected to benefit a lot: no thrashing any more.
It can also help boost I/O throughput for large memory systems, for
VM_MAX_READAHEAD now defaults to 1MB. The value is no longer tightly
coupled with the thrashing problem, and therefore constrainted by it.
Changelog
=========
V10 2005-12-16
- remove delayed page activation
- remove live page protection
- revert mmap readaround to old behavior
- default to original readahead logic
- default to original readahead size
- merge comment fixes from Andreas Mohr
- merge radixtree cleanups from Christoph Lameter
- reduce sizeof(struct file_ra_state) by unnamed union
- stateful method cleanups
- account other read-ahead paths
V9 2005-12-3
- standalone mmap read-around code, a little more smart and tunable
- make stateful method sensible of request size
- decouple readahead_ratio from live pages protection
- let readahead_ratio contribute to ra_size grow speed in stateful method
- account variance of ra_size
V8 2005-11-25
- balance zone aging only in page relaim paths and do it right
- do the aging of slabs in the same way as zones
- add debug code to dump the detailed page reclaim steps
- undo exposing of struct radix_tree_node and uninline related functions
- work better with nfsd
- generalize accelerated context based read-ahead
- account smooth read-ahead aging based on page referenced/activate bits
- avoid divide error in compute_thrashing_threshold()
- more low lantency efforts
- update some comments
- rebase debug actions on debugfs entries instead of magic readahead_ratio values
V7 2005-11-09
- new tunable parameters: readahead_hit_rate/readahead_live_chunk
- support sparse sequential accesses
- delay look-ahead if drive is spinned down in laptop mode
- disable look-ahead for loopback file
- make mandatory thrashing protection more simple and robust
- attempt to improve responsiveness on large read-ahead size
V6 2005-11-01
- cancel look-ahead in laptop mode
- increase read-ahead limit to 0xFFFF pages
V5 2005-10-28
- rewrite context based method to make it clean and robust
- improved accuracy of stateful thrashing threshold estimation
- make page aging equal to the number of code pages scanned
- sort out the thrashing protection logic
- enhanced debug/accounting facilities
V4 2005-10-15
- detect and save live chunks on page reclaim
- support database workload
- support reading backward
- radix tree lookup look-aside cache
V3 2005-10-06
- major code reorganization and documention
- stateful estimation of thrashing-threshold
- context method with accelerated grow up phase
- adaptive look-ahead
- early detection and rescue of pages in danger
- statitics data collection
- synchronized page aging between zones
V2 2005-09-15
- delayed page activation
- look-ahead: towards pipelined read-ahead
V1 2005-09-13
Initial release which features:
o stateless (for now)
o adapts to available memory / read speed
o free of thrashing (in theory)
And handles:
o large number of slow streams (FTP server)
o open/read/close access patterns (NFS server)
o multiple interleaved, sequential streams in one file
(multithread / multimedia / database)
Thanks,
Wu Fengguang
--
Dept. Automation University of Science and Technology of China