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Date:   Tue, 18 Jul 2023 17:16:15 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     "zhangpeng (AS)" <zhangpeng362@huawei.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        sidhartha.kumar@oracle.com, akpm@linux-foundation.org,
        wangkefeng.wang@huawei.com, sunnanyong@huawei.com
Subject: Re: [PATCH 1/6] mm/page_io: use a folio in __end_swap_bio_read()
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On Tue, Jul 18, 2023 at 08:56:16PM +0800, zhangpeng (AS) wrote:
> > >   	if (bio->bi_status) {
> > > -		SetPageError(page);
> > > -		ClearPageUptodate(page);
> > > +		folio_set_error(folio);
> > I appreciate this is a 1:1 conversion, but maybe we could think about
> > this a bit.  Is there anybody who checks the
> > PageError()/folio_test_error() for this page/folio?
> 
> Maybe wait_dev_supers() checks the PageError() after write_dev_supers()
> in fs/btrfs/disk-io.c?

How does _this_ folio end up in btrfs's write_dev_supers()?  This is a
swap read.  The only folios which are swapped are anonymous and tmpfs.
btrfs takes care of doing its own I/O.  wait_dev_supers() is looking
for the error set in btrfs_end_super_write() which is the completion
routine for write_dev_supers().  The pages involved there are attached
to a btrfs address_space, not shmem or anon.