2022-01-24 16:07:57

by NeilBrown

Subject: [PATCH 04/23] MM: move responsibility for setting SWP_FS_OPS to ->swap_activate

If a filesystem wishes to handle all swap IO itself (via ->direct_IO),
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().

Signed-off-by: NeilBrown <[email protected]>
---
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 59334be9ed3b..c795d4a9ec4a 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4974,7 +4974,8 @@ 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 76d76acbc594..d5aa55c7edb0 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 a43929f7033e..b57cff3c5ac2 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -573,6 +573,12 @@ 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 71c7a31dd291..ed6028aea8bf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2347,13 +2347,9 @@ 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;
}

2022-01-24 18:41:21

by Christoph Hellwig

Subject: Re: [PATCH 04/23] MM: move responsibility for setting SWP_FS_OPS to ->swap_activate

On Mon, Jan 24, 2022 at 02:48:32PM +1100, NeilBrown wrote:
> If a filesystem wishes to handle all swap IO itself (via ->direct_IO),

Right now it's half ->direct_IO and half ->readpage and about to change
with your series, isn't it?

> 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().
>
> Signed-off-by: NeilBrown <[email protected]>

Otherwise looks good:

Reviewed-by: Christoph Hellwig <[email protected]>