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Subject: [PATCH 03/10] MM: move responsibility for setting SWP_FS_OPS to
 ->swap_activate
From:   NeilBrown <neilb@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        David Howells <dhowells@redhat.com>, linux-nfs@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Date:   Wed, 30 Mar 2022 10:49:41 +1100
Message-ID: <164859778123.29473.17908205846599043598.stgit@noble.brown>
In-Reply-To: <164859751830.29473.5309689752169286816.stgit@noble.brown>
References: <164859751830.29473.5309689752169286816.stgit@noble.brown>
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If a filesystem wishes to handle all swap IO itself (via ->direct_IO and
->readpage), rather than just providing devices addresses for
submit_bio(), SWP_FS_OPS must be set.
Currently the protocol for setting this it to have ->swap_activate
return zero.  In that case SWP_FS_OPS is set, and add_swap_extent()
is called for the entire file.

This is a little clumsy as different return values for ->swap_activate
have quite different meanings, and it makes it hard to search for which
filesystems require SWP_FS_OPS to be set.

So remove the special meaning of a zero return, and require the
filesystem to set SWP_FS_OPS if it so desires, and to always call
add_swap_extent() as required.

Currently only NFS and CIFS return zero for add_swap_extent().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/cifs/file.c       |    3 ++-
 fs/nfs/file.c        |   13 +++++++++++--
 include/linux/swap.h |    6 ++++++
 mm/swapfile.c        |   10 +++-------
 4 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 60f43bff7ccb..050f463580f3 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4927,7 +4927,8 @@ static int cifs_swap_activate(struct swap_info_struct *sis,
 	 * from reading or writing the file
 	 */
 
-	return 0;
+	sis->flags |= SWP_FS_OPS;
+	return add_swap_extent(sis, 0, sis->max, 0);
 }
 
 static void cifs_swap_deactivate(struct file *file)
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 2df2a5392737..66136dca0ad5 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -488,6 +488,7 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 {
 	unsigned long blocks;
 	long long isize;
+	int ret;
 	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);
 	struct inode *inode = file->f_mapping->host;
 
@@ -500,9 +501,17 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 		return -EINVAL;
 	}
 
+	ret = rpc_clnt_swap_activate(clnt);
+	if (ret)
+		return ret;
+	ret = add_swap_extent(sis, 0, sis->max, 0);
+	if (ret < 0) {
+		rpc_clnt_swap_deactivate(clnt);
+		return ret;
+	}
 	*span = sis->pages;
-
-	return rpc_clnt_swap_activate(clnt);
+	sis->flags |= SWP_FS_OPS;
+	return ret;
 }
 
 static void nfs_swap_deactivate(struct file *file)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 6bc9e21262de..e18b7edccc1d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -570,6 +570,12 @@ static inline swp_entry_t get_swap_page(struct page *page)
 	return entry;
 }
 
+static inline int add_swap_extent(struct swap_info_struct *sis,
+				  unsigned long start_page,
+				  unsigned long nr_pages, sector_t start_block)
+{
+	return -EINVAL;
+}
 #endif /* CONFIG_SWAP */
 
 #ifdef CONFIG_THP_SWAP
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2650927a009b..8710c9c29862 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2244,13 +2244,9 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 
 	if (mapping->a_ops->swap_activate) {
 		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
-		if (ret >= 0)
-			sis->flags |= SWP_ACTIVATED;
-		if (!ret) {
-			sis->flags |= SWP_FS_OPS;
-			ret = add_swap_extent(sis, 0, sis->max, 0);
-			*span = sis->pages;
-		}
+		if (ret < 0)
+			return ret;
+		sis->flags |= SWP_ACTIVATED;
 		return ret;
 	}