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| * [http://www.cs.wm.edu/hpcs/WWW/HTML/publications/abs05-3.html CLOCK-Pro] an effective improvement of the CLOCK replacement. | * [http://www.cs.wm.edu/hpcs/WWW/HTML/publications/abs05-3.html CLOCK-Pro] an effective improvement of the CLOCK replacement, and the ClockProApproximation that Rik van Riel is planning to implement. |
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| Rik's interface (for implementation, see NonResidentPages): | Rik's interface (for implementation, see NonResidentPages, code and patches on [http://surriel.com/patches/nonresident my home page]): |
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| * Keeps track of whether a non-resident page was recently evicted * and should be immediately promoted to the active/frequency list. * * The pageout code stores a recently evicted page in this cache * by calling remember_page(mapping/mm, offset/vaddr, generation) * and can look it up in the cache by calling recently_evicted() * with the same arguments. */ extern int recently_evicted(void * mapping, unsigned long index, short flag); extern void remember_page(void * mapping, unsigned long index, short flag); |
extern int recently_evicted(void * mapping, unsigned long index); extern int remember_page(void * mapping, unsigned long index); |
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The ''recently_evicted'' function is queried by the pagein or page cache allocation code, to determine whether the data at the offset ''index'' from the page cache or process object ''mapping'' was recently evicted. The function returns 0 if the page was not found, 1 if the page was found. The ''remember_page'' function is called by the pageout code, telling the non-resident page management code to remember that a page at offset ''index'' from ''mapping'' was just paged out. We use a hash of ''mapping->host->i_ino'' and ''mapping->host->i_sb'' (and/or possibly other fields) to keep things unique. |
LRU has been obsoleted by large address spaces, streaming media and garbage collection, but until 2002 there weren't many replacements available that are suitable to be implemented in a general purpose OS. However, with the advent of LIRS, ARC, Clock-pro and CAR/CART algorithms, it looks like there could be a benefit to Linux in implementing something better than LRU or the unbalanced use-once that is in use currently.
The only problem is, the advanced page replacement algorithms need to keep a history of recently evicted pages, and we don't want to spend too much memory or cpu on that. This page is a template for brainstorming on how we can implement such a framework, and on which of the advanced page replacement algorithms we should experiment with.
Please feel free to edit this page, after having created an account.
The replacement algorithms
[http://www.almaden.ibm.com/StorageSystems/autonomic_storage/ARC/index.shtml ARC] Adaptive Replacement Cache.
[http://www.cs.wm.edu/~sjiang/lirs.htm LIRS] Low Inter-Reference Recency Set.
[http://www.cs.wm.edu/hpcs/WWW/HTML/publications/abs05-3.html CLOCK-Pro] an effective improvement of the CLOCK replacement, and the ClockProApproximation that Rik van Riel is planning to implement.
[http://www.almaden.ibm.com/cs/people/dmodha/clockfast.pdf CAR] Clock with Adaptive Replacement.
Proposals for dealing with non-resident pages
Rik's interface (for implementation, see NonResidentPages, code and patches on [http://surriel.com/patches/nonresident my home page]):
extern int recently_evicted(void * mapping, unsigned long index); extern int remember_page(void * mapping, unsigned long index);
The recently_evicted function is queried by the pagein or page cache allocation code, to determine whether the data at the offset index from the page cache or process object mapping was recently evicted. The function returns 0 if the page was not found, 1 if the page was found.
The remember_page function is called by the pageout code, telling the non-resident page management code to remember that a page at offset index from mapping was just paged out.
We use a hash of mapping->host->i_ino and mapping->host->i_sb (and/or possibly other fields) to keep things unique.