Re: Heuristic readahead for filesystems

[jw schultz <jw@pegasys.ws>]

On Wed, Sep 11, 2002 at 03:21:37PM -0400, Richard B. Johnson wrote:
> On Wed, 11 Sep 2002, Oliver Neukum wrote:
> > Am Mittwoch, 11. September 2002 20:43 schrieb Xuan Baldauf:

> > > > Aio should be able to do it. But even that want help you with the stat
> > > > data.
> > >
> > > Aio would help me announcing stat() usage for the future?
> > 
> > No, it won't. But it would solve the issue of reading ahead.
> > Stating needs a kernel implementation of 'stat ahead'
> > -
> 
> I think this is discussed in the future. Write-ahead is the
> next problem solved. ?;)

Gating back to the original issue which was "readahead" of
stat() info...

The userland open of a directory could trigger an advance
reading of the directory data and of the inode structs of
all it's immediate members.  Almost all instances of a
usermode open on a directory will be doing fstats.  Even a
command line ls often has options (colour, -F, etc) turned on
by default that require fstat on all the entries.
The question would be how far ahead of the user app would
the kernel be.

I could possibly see having a fcntl() for directories to
pre-read just the first block of each file to accelerate
file-managers that use magic and perhaps forestall readahead
pulling in more than magic will use.

-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw@pegasys.ws

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