Date: Wed, 02 Sep 1998 18:48:21 +0000 From: Mike Smith <mike@smith.net.au> To: Terry Lambert <tlambert@primenet.com> Cc: cmascott@world.std.com (Carl Mascott), hackers@FreeBSD.ORG Subject: Re: Reading/writing /usr/ports is VERY slow Message-ID: <199809021848.SAA01527@dingo.cdrom.com> In-Reply-To: Your message of "Thu, 03 Sep 1998 01:12:26 GMT." <199809030112.SAA02792@usr07.primenet.com>
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> > However, > > if a cg proximity criterion were added to the new-cg-chooser, > > then the size of a cg would become a factor, although I don't > > know how important a factor. > > Very important. It would result in FFS finally adding "support" > for fragmenting the bejesus out of a disk drive. > > This would be a *very* bad thing. Could you explain how the proposed change would do this? It's no worse than the current case if there is one cg with substantially fewer directories than any other. In fact, you could simplify the code somewhat just by lying about the number of directories in the cg referenced by the rotor. > > Hopefully someone who knows the history of FFS development > > will chime in at this point. It would be nice to know if > > any other directory placement policies were ever tried and > > rejected. > > The original "free reserve" values were set to 10% for a reason; it > was a compromise between people who wanted to use every byte, and > the actual 15% value required for a "perfect hash". The change I proposed honours the reserve. Now I *know* you didn't look at it. 8) > In effect, when the FS picks a block (or, more correctly, a cluster), > it is hashing the filespace onto the disk. Unfortunately, in the case of directories this results in them being scattered all over the disk. If you're creating a pile of them all at once in a hierarchy, the net result is very poor locality of reference. Associating locality and time of creation is not a wonderful algorithm, I freely admit. However, I think that it has some merit over the current approach (forcibly minimise locality under some circumstances). If you have the stuff set up to test, I'd really be interested to see if the clustering I proposed demonstrated any effects. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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