[lkml]   [2001]   [Sep]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: linux-2.4.10-pre5
On September 11, 2001 05:48 pm, Linus Torvalds wrote:
> On Tue, 11 Sep 2001, Daniel Phillips wrote:
> >
> > But see my post in this thread where I created a simple test to show that,
> > even when we pre-read *all* the inodes in a directory, there is no great
> > performance win.
> Note that I suspect that because the inode tree _is_ fairly dense, you
> don't actually need to do much read-ahead in most cases. Simply because
> you automatically do read-ahead _always_: when somebody reads a 128-byte
> inode, you (whether you like it or not) always "read-ahead" the 31 inodes
> around it on a 4kB filesystem.
> So we _already_ do read-ahead by a "factor of 31". Whether we can improve
> that or not by increasing it to 63 inodes, who knows?
> I actually think that the "start read-ahead for inode blocks when you do
> readdir" might be a bigger win, because that would be a _new_ kind of
> read-ahead that we haven't done before, and might improve performance for
> things like "ls -l" in the cold-cache situation..

But wait, if our theories are correct then the disk is doing physical
readahead anyway, and its a nice scsi disk with lots of cache, so *why does
it take so long to read the metadata*? It's about 11,000 files, that's
1.3Meg of inodes and just a couple hundred K of directories.

There is clearly something nonoptimal about the hardware readahead and/or

> (Although again, because the inode is relatively small to the IO cache
> size, it's probably fairly _hard_ to get a fully cold-cache inode case. So
> I'm not sure even that kind of read-ahead would actually make any
> difference at all).

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:03    [W:0.081 / U:1.384 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site