Re: [RFC PATCH] mm, netfs: Provide a means of invalidation without using launder_folio

[Matthew Wilcox <willy@infradead.org>]

On Wed, Mar 27, 2024 at 03:56:50PM +0000, Trond Myklebust wrote:
> On Wed, 2024-03-27 at 15:04 +0000, David Howells wrote:
> > Implement a replacement for launder_folio[1].  The key feature of
> > invalidate_inode_pages2() is that it locks each folio individually,
> > unmaps
> > it to prevent mmap'd accesses interfering and calls the -
> > >launder_folio()
> > address_space op to flush it.  This has problems: firstly, each folio
> > is
> > written individually as one or more small writes; secondly, adjacent
> > folios
> > cannot be added so easily into the laundry; thirdly, it's yet another
> > op to
> > implement.
> 
> This is hardly a drop-in replacement for launder_page. The whole point
> of using invalidate_inode_pages2() was that it only requires taking the
> page locks, allowing us to use it in contexts such as
> nfs_release_file().
> 
> The above use of truncate_inode_pages_range() will require any caller
> to grab several locks in order to prevent data loss through races with
> write system calls.

I don't understand why you need launder_folio now
that you have a page_mkwrite implementation (your commit
e3db7691e9f3dff3289f64e3d98583e28afe03db used this as justification).
Other filesystems (except the network filesystems that copied the NFS
implementation) don't implement launder_folio.