On Wed, Apr 21, 2010 at 07:51:24PM +0100, Jamie Lokier (jamie@xxxxxxxxxxxxx) wrote: > Fwiw, I found sorting directories by inode and reading them in that > order help to reduce seeks, some 10 years ago. I implemented > something like 'find' which works like that, keeping a queue of > directories to read and things to open/stat, ordered by inode number > seen in d_ino before open/stat and st_ino after. However it did not > try to readahead the blocks inside a directory, or sort operations by > block number. It reduced some 'find'-like operations to about a > quarter of the time on cold cache. I still use that program sometimes > before "git status" ;-) Google "treescan" and "lokier" if you're > interested in trying it (though I use 0.7 which isn't published). As you might expect it is not really a directory readahead :) Nad I'm not really sure ext234 can implement it in kernel more optimally without breaking backward compatibility though. > > it is not about readdir(). Plain read() is synchronous too. But > > filesystem can respond to readahead calls and read next block to current > > one, while it won't do this for next direntry. > > I'm surprised it makes much difference, as directories are usually not > very large anyway. Well, having several tens of millions of files in 64k dirs takes from tens of seconds to minutes to read just because of that. > But if it does, go on, try FIEMAP and blockdev reading, you know you > want to :-) Well, it requires substantial underlying fs knowledge and is not simple and, well, appropriate to do in some cases. -- Evgeniy Polyakov -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
