> What would perhaps be better than a hardcoded reclaim age would be to use > an LRU-type approach and perhaps set a target percent to reclaim. That is, > suppose you were to reclaim the oldest 10% of hashes on each lowmem call > (and make the '10%' the tunable value). Then you will always make some amount > of progress in a low memory situation (and if the situation remains dire you > will eventually empty the entire cache), but the effective maximum age will > be more dynamic. Right now if you haven't touched UFS in 5 seconds it > throws the entire thing out on the first lowmem event. The LRU-approach would > only throw the oldest 10% out on the first call, but eventually throw it all > out > if the situation remains dire. > > -- > John Baldwin > _______________________________________________ > freebsd...@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscr...@freebsd.org"
I liked your idea more than what's available in HEAD right now and I implemented it. http://people.freebsd.org/~davide/review/ufs_direclaimage.diff I was unsure what kind of heuristic I should choose to select which (10% of) entries should be evicted so I just removed the first 10% ones from the head of the ufs_dirhash list (which should be the oldest). The code keeps rescanning the cache until 10% (or, the percentage set via SYSCTL) of the entry are freed, but probably we can discuss if this limit could be relaxed and just do a single scan over the list. Unfortunately I haven't a testcase to prove the effectiveness (or non-effectiveness) of the approach but I think either Ivan or Peter could be able to give it a spin, maybe. -- Davide "There are no solved problems; there are only problems that are more or less solved" -- Henri Poincare _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
