Re: [PATCH 04/26] xfs: Improve metadata buffer reclaim accountability

Dave Chinner
2019-10-11T23:13:30Z

On Fri, Oct 11, 2019 at 08:39:39AM -0400, Brian Foster wrote:
> On Wed, Oct 09, 2019 at 02:21:02PM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > The buffer cache shrinker frees more than just the xfs_buf slab
> > objects - it also frees the pages attached to the buffers. Make sure
> > the memory reclaim code accounts for this memory being freed
> > correctly, similar to how the inode shrinker accounts for pages
> > freed from the page cache due to mapping invalidation.
> >
> > We also need to make sure that the mm subsystem knows these are
> > reclaimable objects. We provide the memory reclaim subsystem with a
> > a shrinker to reclaim xfs_bufs, so we should really mark the slab
> > that way.
> >
> > We also have a lot of xfs_bufs in a busy system, spread them around
> > like we do inodes.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
>
> Seems reasonable, but for inodes we also spread the ili zone. Should we
> not be consistent with bli's as well?

bli's are reclaimed when the buffer is cleaned. ili's live for the
live of the inode in cache. Hence bli's are short term allocations
(much shorter than xfs_bufs they attach to) and are reclaimed much
faster than inodes and their ilis. There's also a lot less blis than
ili's, so the spread of their footprint across memory nodes doesn't
matter that much. Local access for the memcpy during formatting is
probably more important than spreading the memory usage of them
these days, anyway.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com