Date: Thu, 10 Oct 2013 16:29:56 -0400 From: John Baldwin <jhb@freebsd.org> To: Davide Italiano <davide@freebsd.org> Cc: Kirk McKusick <mckusick@freebsd.org>, alc@freebsd.org, freebsd-hackers <freebsd-hackers@freebsd.org>, freebsd-fs@freebsd.org, Ivan Voras <ivoras@freebsd.org>, pho@freebsd.org Subject: Re: Call fo comments - raising vfs.ufs.dirhash_reclaimage? Message-ID: <201310101629.56289.jhb@freebsd.org> In-Reply-To: <CACYV=-GZPbC03stS6PsihfJ688kbjna2-n0%2BPdctr3L9hvSvag@mail.gmail.com> References: <kvkvi7$iv7$1@ger.gmane.org> <201309031507.33098.jhb@freebsd.org> <CACYV=-GZPbC03stS6PsihfJ688kbjna2-n0%2BPdctr3L9hvSvag@mail.gmail.com>
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On Monday, October 07, 2013 1:34:24 pm Davide Italiano wrote: > > 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-fs@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@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. I think this looks good. One cosmetic nit is that I think this: if (!try_lock()) continue; else memfreed += ufsdirhash_destroy(); Looks a bit odd. I would either drop the else (which the old code did in its failsafe case) or just do this: if (try_lock()) memfreed += ufsdirhash_destroy(); -- John Baldwin
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