+ mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: move responsibility for setting SWP_FS_OPS to ->swap_activate
has been added to the -mm tree.  Its filename is
     mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch

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------------------------------------------------------
From: NeilBrown <neilb@suse.de>
Subject: mm: move responsibility for setting SWP_FS_OPS to ->swap_activate

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().

Link: https://lkml.kernel.org/r/164859778123.29473.17908205846599043598.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/cifs/file.c       |    3 ++-
 fs/nfs/file.c        |   14 ++++++++++++--
 include/linux/swap.h |    6 ++++++
 mm/swapfile.c        |   10 +++-------
 4 files changed, 23 insertions(+), 10 deletions(-)

--- a/fs/cifs/file.c~mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate
+++ a/fs/cifs/file.c
@@ -4927,7 +4927,8 @@ static int cifs_swap_activate(struct swa
 	 * 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)
--- a/fs/nfs/file.c~mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate
+++ a/fs/nfs/file.c
@@ -483,6 +483,7 @@ static int nfs_swap_activate(struct swap
 {
 	unsigned long blocks;
 	long long isize;
+	int ret;
 	struct inode *inode = file_inode(file);
 	struct rpc_clnt *clnt = NFS_CLIENT(inode);
 	struct nfs_client *cl = NFS_SERVER(inode)->nfs_client;
@@ -496,13 +497,22 @@ static int nfs_swap_activate(struct swap
 		return -EINVAL;
 	}
 
-	*span = sis->pages;
+	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;
 
 	if (cl->rpc_ops->enable_swap)
 		cl->rpc_ops->enable_swap(inode);
 
-	return rpc_clnt_swap_activate(clnt);
+	sis->flags |= SWP_FS_OPS;
+	return ret;
 }
 
 static void nfs_swap_deactivate(struct file *file)
--- a/include/linux/swap.h~mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate
+++ a/include/linux/swap.h
@@ -570,6 +570,12 @@ static inline swp_entry_t get_swap_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
--- a/mm/swapfile.c~mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate
+++ a/mm/swapfile.c
@@ -2244,13 +2244,9 @@ static int setup_swap_extents(struct swa
 
 	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;
 	}
 
_

Patches currently in -mm which might be from neilb@suse.de are

mm-create-new-mm-swaph-header-file.patch
mm-drop-swap_dirty_folio.patch
mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch
mm-reclaim-mustnt-enter-fs-for-swp_fs_ops-swap-space.patch
mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space.patch
mm-perform-async-writes-to-swp_fs_ops-swap-space-using-swap_rw.patch
doc-update-documentation-for-swap_activate-and-swap_rw.patch
mm-submit-multipage-reads-for-swp_fs_ops-swap-space.patch
mm-submit-multipage-write-for-swp_fs_ops-swap-space.patch
vfs-add-fmode_can_odirect-file-flag.patch
mm-discard-__gfp_atomic.patch