Re: [PATCH 11/14] xfs: dynamically allocate cursors based on maxlevels

Darrick J. Wong
2021-09-22T18:55:56Z

On Tue, Sep 21, 2021 at 10:03:49AM +0100, Christoph Hellwig wrote:
> On Tue, Sep 21, 2021 at 09:06:35AM +1000, Dave Chinner wrote:
> > On Fri, Sep 17, 2021 at 06:30:10PM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <djwong@kernel.org>
> > >
> > > Replace the statically-sized btree cursor zone with dynamically sized
> > > allocations so that we can reduce the memory overhead for per-AG bt
> > > cursors while handling very tall btrees for rt metadata.
> >
> > Hmmmmm. We do a *lot* of btree cursor allocation and freeing under
> > load. Keeping that in a single slab rather than using heap memory is
> > a good idea for stuff like this for many reasons...
>
> Or rather a few slabs for the different kind of cursors. But otherwise
> agreed.

I think I prefer to let Chandan decide if there are going to be enough
heavily fragmented files to warrant a second slab for maxlevels>9 files.
We should probably be selective about which cursor maxheight we want to
use depending on whether or not the file really needs it.

--D