Date: Tue, 03 Jun 2008 12:46:43 +0300 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Garance A Drosihn <drosih@rpi.edu> Cc: freebsd-hackers@freebsd.org, ssouhlal@freebsd.org Subject: Re: Impact of having a large number of open file descriptors Message-ID: <87prqykfzw.fsf@kobe.laptop> In-Reply-To: <p06240802c46a3f7d58a8@[128.113.124.153]> (Garance A. Drosihn's message of "Mon\, 2 Jun 2008 21\:07\:15 -0400") References: <200805281446.m4SEkojn099133@lurza.secnetix.de> <64200F15-4444-44FE-B904-673543441F35@FreeBSD.org> <g21p5m$g1l$1@ger.gmane.org> <4844751C.80704@FreeBSD.org> <p06240802c46a3f7d58a8@[128.113.124.153]>
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On Mon, 2 Jun 2008 21:07:15 -0400, Garance A Drosihn <drosih@rpi.edu> wrote: > At 12:33 AM +0200 6/3/08, Kris Kennaway wrote: >>Ivan Voras wrote: >>>Suleiman Souhlal wrote: >>> >>>> I have an old patch that makes kqueue monitor every file write on >>>> the system and return the inode number in the knote's data field: >>>> http://people.freebsd.org/~ssouhlal/testing/kqueue-anyvnode-20050503.diff >>>> . >>>> >>>>I'd think it shouldn't be too hard to make it per-mountpoint.. >> >> FWIW, I would love to use this. I have situations where I have huge >> numbers of files and need to cheaply detect changes so I can >> resynchronize them to remote machines. > > I remember a discussion of changes to MacOS10 in Leopard which made it > easier to implement features such as Spotlight and TimeMachine. The > description starts here, I think: > > http://arstechnica.com/reviews/os/mac-os-x-10-5.ars/7 > > the section on file-system events. > > The idea I thought was interesting was to save the metadata on a > directory basis, instead of saving it on the file. So, if file > /some/dir/fname was changed, then they'd record that *some* file under > /some/dir has changed. > > So when your userland process comes along later on, it still has to > scan all files in that directory to see which file(s) actually > changed. But that's a lot less work than scanning all files in the > filesystem, and it also means there is much less data that has to be > kept track of. > > I have no idea how easy it would be to implement something similar on > FreeBSD, but the strategy seemed like a pretty neat idea. It sounds like a useful compromise between the number of tracked entries and scanning the entire fs :)
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