linux-kernel - Re: [RFC PATCH v2] mm, netfs: Provide a means of invalidation without using launder

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Message-ID: <2541308.1711571866@warthog.procyon.org.uk>
Date: Wed, 27 Mar 2024 20:37:46 +0000
From: David Howells <dhowells@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: dhowells@...hat.com, Miklos Szeredi <miklos@...redi.hu>,
    Trond Myklebust <trond.myklebust@...merspace.com>,
    Christoph Hellwig <hch@....de>,
    Andrew Morton <akpm@...ux-foundation.org>,
    Alexander Viro <viro@...iv.linux.org.uk>,
    Christian Brauner <brauner@...nel.org>,
    Jeff Layton <jlayton@...nel.org>, linux-mm@...ck.org,
    linux-fsdevel@...r.kernel.org, netfs@...ts.linux.dev,
    v9fs@...ts.linux.dev, linux-afs@...ts.infradead.org,
    ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
    linux-nfs@...r.kernel.org, devel@...ts.orangefs.org,
    linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] mm, netfs: Provide a means of invalidation without using launder_folio

Matthew Wilcox <willy@...radead.org> wrote:

> > +	/* Prevent new folios from being added to the inode. */
> > +	filemap_invalidate_lock(mapping);
> 
> I'm kind of surprised that the callers wouldn't want to hold that lock
> over a call to this function.  I guess you're working on the callers,
> so you'd know better than I would, but I would have used lockdep to
> assert that invalidate_lock was held.

I'm not sure.  None of the places that look like they'd be calling this
currently take that lock (though possibly they should).

Also, should I provide it with explicit range, I wonder?

> > +	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
> > +		unmap_mapping_pages(mapping, 0, ULONG_MAX, false);
> 
> Is this optimisation worth it?

Perhaps not.

David