linux-kernel - Re: [RFC PATCH 3/9] btrfs: use set/clear_fs_page

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Date:   Mon, 27 Apr 2020 14:27:41 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dave Chinner <david@...morbit.com>,
        Guoqing Jiang <guoqing.jiang@...ud.ionos.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        willy@...radead.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org
Subject: Re: [RFC PATCH 3/9] btrfs: use set/clear_fs_page_private

On Sun, Apr 26, 2020 at 10:54:28PM -0700, Christoph Hellwig wrote:
> On Mon, Apr 27, 2020 at 08:20:54AM +1000, Dave Chinner wrote:
> > >  void set_page_extent_mapped(struct page *page)
> > >  {
> > > -	if (!PagePrivate(page)) {
> > > -		SetPagePrivate(page);
> > > -		get_page(page);
> > > -		set_page_private(page, EXTENT_PAGE_PRIVATE);
> > > -	}
> > > +	if (!PagePrivate(page))
> > > +		set_fs_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
> > 
> > Change the definition of EXTENT_PAGE_PRIVATE so the cast is not
> > needed? Nothing ever reads EXTENT_PAGE_PRIVATE; it's only there to
> > set the private flag for other code to check and release the extent
> > mapping reference to the page...
> 
> IIRC there as a patch on the btrfs list to remove EXTENT_PAGE_PRIVATE,
> it might be better to not bother changing it.  Maybe the btrfs
> maintainers remember this better.

The patch removing it is part of patchset adding full iomap support to
btrfs,
(https://lore.kernel.org/linux-btrfs/20190905150650.21089-4-rgoldwyn@suse.de/)
but it'll still take some time so I'm OK with using the
set_fs_page_private helper and adding the cast to EXTENT_PAGE_PRIVATE
definition.