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Date:   Mon, 17 Jan 2022 13:47:17 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     ceph-devel@vger.kernel.org, jlayton@kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/3] ceph: Uninline the data on a file opened for writing
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On Mon, Jan 17, 2022 at 12:44:33PM +0000, David Howells wrote:
> +	if (ceph_caps_issued(ci) & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) {
> +		folio = filemap_get_folio(inode->i_mapping, 0);
> +		if (folio) {
> +			if (folio_test_uptodate(folio)) {
>  				from_pagecache = true;
> -				lock_page(page);
> +				folio_lock(folio);
>  			} else {
> -				put_page(page);
> -				page = NULL;
> +				folio_put(folio);
> +				folio = NULL;

This all falls very much under "doing it the hard way", and quite
possibly under the "actively buggy with races" category.

read_mapping_folio() does what you want, as long as you pass 'filp'
as your 'void *data'.  I should fix that type ...