Re: [PATCH 2/2] fs: Do not update nr_thps for mappings which support THPs

[Matthew Wilcox]

On Wed, Sep 16, 2020 at 06:21:26AM +0100, Christoph Hellwig wrote:
> On Wed, Sep 16, 2020 at 04:27:17AM +0100, Matthew Wilcox (Oracle) wrote:
> > The nr_thps counter is to support THPs in the page cache when the
> > filesystem doesn't understand THPs.  Eventually it will be removed, but
> > we should still support filesystems which do not understand THPs yet.
> > Move the nr_thp manipulation functions to filemap.h since they're
> > page-cache specific.
> 
> Honestly I don't think we should support the read-only THP crap.  We
> should in fact never have merged that bandaid to start with given that
> you did good progress on the real thing.

I'd like to see the feature ripped out again, yes.  Once we have a few more
filesystems converted, I think that'll be a reasonable thing to do.

It was a good step along the way; Song fixed a number of problems,
and worked on other things that I never had to learn anything about
(like uprobes and khugepaged).  I wouldn't go so far as to say we should
never have merged it, but I think we can remove it in about six months.