RE: [rfc] lockless pagecache

Badari Pulavarty
2005-06-27T18:51:22Z

On Mon, 2005-06-27 at 11:14 -0700, Chen, Kenneth W wrote:
> Nick Piggin wrote on Monday, June 27, 2005 2:04 AM
> > >> However I think for Oracle and others that use shared memory like
> > >> this, they are probably not doing linear access, so that would be a
> > >> net loss. I'm not completely sure (I don't have access to real loads
> > >> at the moment), but I would have thought those guys would have looked
> > >> into fault ahead if it were a possibility.
> > >
> > >
> > > i thought those guys used O_DIRECT - in which case, wouldn't the page
> > > cache not be used?
> > >
> >
> > Well I think they do use O_DIRECT for their IO, but they need to
> > use the Linux pagecache for their shared memory - that shared
> > memory being the basis for their page cache. I think. Whatever
> > the setup I believe they have issues with the tree_lock, which is
> > why it was changed to an rwlock.
>
> Typically shared memory is used as db buffer cache, and O_DIRECT is
> performed on these buffer cache (hence O_DIRECT on the shared memory).
> You must be thinking some other workload. Nevertheless, for OLTP type
> of db workload, tree_lock hasn't been a problem so far.

What about DSS ? I need to go back and verify some of the profiles
we have.

Thanks,
Badari