Uncached stat performace [ Was: Re: Kernel SCM saga.. ]

[Ragnar Kjørstad]

On Fri, Apr 08, 2005 at 12:39:26PM -0700, Linus Torvalds wrote:
> One of the reasons I do inode numbers in the "index" file (apart from 
> checking that the inode hasn't changed) is in fact that "stat()" is damn 
> slow if it causes seeks. Since your stat loop is entirely 
> 
> You can optimize your stat() patterns on traditional unix-like filesystems
> by just sorting the stats by inode number (since the inode number is
> historically a special index into the inode table - even when filesystems
> distribute the inodes over several tables, sorting will generally do the
> right thing from a seek perspective). It's a disgusting hack, but it
> literally gets you orders-of-magnitude performance improvments in many
> real-life cases.

It does, so why isn't there a way to do this without the disgusting
hack? (Your words, not mine :) )

E.g, wouldn't a aio_stat() allow simular or better speedups in a way
that doesn't depend on ext2/3 internals?

I bet it would make a significant difference from things like "ls -l" in
large uncached directories and imap-servers with maildir?



-- 
Ragnar Kjørstad
Software Engineer
Scali - http://www.scali.com
Scaling the Linux Datacenter
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