linux-kernel - Re: [PATCH 3/6] iomap: Use __set_page_dirty

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Message-ID: <YMomnpDT9EQ/5XB9@casper.infradead.org>
Date:   Wed, 16 Jun 2021 17:28:14 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] iomap: Use __set_page_dirty_nobuffers

On Wed, Jun 16, 2021 at 08:50:40AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 15, 2021 at 07:13:16PM +0100, Matthew Wilcox wrote:
> > On Tue, Jun 15, 2021 at 07:34:53PM +0200, Christoph Hellwig wrote:
> > > Eventually everything around set_page_dirty should be changed to operate
> > > on folios, and that will be a good time to come up with a sane
> > > naming scheme without introducing extra churn.
> > 
> > The way it currently looks in my tree ...
> > 
> > set_page_dirty(page) is a thin wrapper that calls folio_mark_dirty(folio).
> > folio_mark_dirty() calls a_ops->dirty_folio(mapping, folio) (which
> > 	returns bool).
> > __set_page_dirty_nobuffers() becomes filemap_dirty_folio()
> > __set_page_dirty_buffers() becomes block_dirty_folio()
> > __set_page_dirty_no_writeback() becomes dirty_folio_no_writeback()
> > 
> > Now I look at it, maybe that last should be nowb_dirty_folio().
> 
> Not to be a pain, but you are mixing "folio" at the front and back of
> the api name?  We messed up in the driver core with this for some things
> (get_device() being one), I would recommend just sticking with one
> naming scheme now as you are getting to pick what you want to use.

That is mostly what I'm doing.  eg,

get_page -> folio_get
lock_page -> folio_lock
PageUptodate -> folio_uptodate
set_page_dirty -> folio_mark_dirty

What I haven't dealt with yet is the naming of the
address_space_operations.  My thinking with those is that they should
be verb_folio, since they _aren't_ the functions that get called.
ie it looks like this:

folio_mark_dirty()
  aops->dirty_folio()
    ext4_dirty_folio()
      buffer_dirty_folio()

I actually see the inconsistency here as a good thing -- these are
implementations of the aop, so foo_verb_folio() means you're doing
something weird and internal instead of going through the vfs/mm.

That implies doing things like renaming ->readpage to ->read_folio, but
if we're changing the API from passing a struct page to a struct folio,
that can all be done at the same time with no additional disruption.