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Date: Mon, 23 Apr 2007 20:19:34 -0400 From: Theodore Tso <tytso@....edu> To: "H. Peter Anvin" <hpa@...or.com> Cc: Eric Hopper <hopper@...ifarious.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org Subject: Re: Question about Reiser4 On Mon, Apr 23, 2007 at 04:53:03PM -0700, H. Peter Anvin wrote: > Theodore Tso wrote: > > > >One of the big problems of using a filesystem as a DB is the system > >call overheads. If you use huge numbers of tiny files, then each > >attempt read an atom of information from the DB takes three system > >calls --- an open(), read(), and close(), with all of the overheads in > >terms of dentry and inode cache. > > > > Now, to be fair, there are probably a number of cases where > open/lseek/readv/close and open/lseek/writev/close would be worth doing > as a single system call. The big problem as far as I can see involves > EINTR handling; such a system call has serious restartability implications. Sure, but Hans wants to change /etc/inetd.conf into /etc/inetd.conf.d, where you have: /etc/inetd.conf.d/telnet/port, /etc/inetd.conf.d/telnet/protocol, /etc/inetd.conf.d/telnet/wait, /etc/inetd.conf.d/telnet/userid, /etc/inetd.conf.d/telnet/daemon, etc. for each individual line in /etc/inetd.conf. (And where each file might only contains 2-4 characters each: i.e., "23", "tcp", "root", etc.) So it's not enough just to collapse open/pread/close into a single system call; in order to gain back the performance squandered by all of these itsy-bitsy tiny little files. You want to collapse the open/pread/close for many of these little files into a single system call, hence Hans's insistence on sys_reiser4(); otherwise his scheme doesn't work all that well at all. - Ted - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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