linux-kernel - Re: linux-next: manual merge of the mm-stable tree with the cifs tree

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Message-ID: <2887475.1676991926@warthog.procyon.org.uk>
Date:   Tue, 21 Feb 2023 15:05:26 +0000
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, Stephen Rothwell <sfr@...b.auug.org.au>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steve French <smfrench@...il.com>,
        Steve French <stfrench@...rosoft.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Tom Talpey <tom@...pey.com>, Paulo Alcantara <pc@....nz>,
        Jeff Layton <jlayton@...nel.org>, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-next@...r.kernel.org
Subject: Re: linux-next: manual merge of the mm-stable tree with the cifs tree

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

> > +			start = folio_pos(folio); /* May regress with THPs */
> 
> What does this comment mean?

"start" may end up going backwards if it's pointing to the middle of a folio.

> > +			/* At this point we hold neither the i_pages lock nor the
> > +			 * page lock: the page may be truncated or invalidated
> > +			 * (changing page->mapping to NULL), or even swizzled
> > +			 * back from swapper_space to tmpfs file mapping
> 
> Where does this comment come from?  This is cifs, not tmpfs.  You'll
> never be asked to writeback a page from the swap cache.  Dirty pages
> can be truncated, so the first half of the comment is still accurate.
> I'd rather it moved down to below the folio lock, and was rephrased
> so it described why we're checking everything again.

I picked it up into afs from somewhere - nfs maybe?  The same comment is in
fs/btrfs/extent_io.c.  grep for 'swizzled' in fs/.  You modified the comment
in b93b016313b3ba8003c3b8bb71f569af91f19fc7 in 2018, so it's been around a
while.

David