Currently swapfiles are managed entirely by the core VM by using
->bmap to allocate space and write to the blocks directly. This
patch adds address_space_operations methods that allow a filesystem
to optionally control the swapfile.
int swap_activate(struct file *);
int swap_deactivate(struct file *);
int swap_writepage(struct file *, struct page *, struct writeback_control *);
int swap_readpage(struct file *, struct page *);
The ->swap_activate() method is used to communicate to the file
that the VM relies on it, and the address_space should take adequate
measures such as reserving space in the underlying device, reserving
memory for mempools etc. The ->swap_deactivate() method is called on
sys_swapoff() if ->swap_activate() returned success.
After a successful swapfile ->swap_activate, the swapfile
is marked SWP_FILE and swapper_space.a_ops will proxy to
sis->swap_file->f_mappings->a_ops using ->swap_readpage and
->swap_writepage tp read/write swapcache pages.
The primary user of this interface is expected to be NFS for supporting
swap-over-NFS which is why the existing readpage/writepage interface
is not used. For writing a swap page on NFS, the struct file * is
needed for a credential context that is not passed into writepage.
[a.p.zijlstra@xxxxxxxxx: Original patch]
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
Documentation/filesystems/Locking | 23 +++++++++++++++++++++++
Documentation/filesystems/vfs.txt | 21 +++++++++++++++++++++
include/linux/fs.h | 7 +++++++
include/linux/swap.h | 3 +++
mm/page_io.c | 37 +++++++++++++++++++++++++++++++++++++
mm/swap_state.c | 2 +-
mm/swapfile.c | 30 ++++++++++++++++++++++++++++--
7 files changed, 120 insertions(+), 3 deletions(-)
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 6533807..7f534f4 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -201,6 +201,10 @@ prototypes:
int (*launder_page)(struct page *);
int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
int (*error_remove_page)(struct address_space *, struct page *);
+ int (*swap_activate)(struct file *);
+ int (*swap_deactivate)(struct file *);
+ int (*swap_out)(struct file *, struct page *, struct writeback_control *);
+ int (*swap_in)(struct file *, struct page *);
locking rules:
All except set_page_dirty and freepage may block
@@ -224,6 +228,10 @@ migratepage: yes (both)
launder_page: yes
is_partially_uptodate: yes
error_remove_page: yes
+swap_activate: no
+swap_deactivate: no
+swap_out no yes, unlocks
+swap_in no yes, unlocks
->write_begin(), ->write_end(), ->sync_page() and ->readpage()
may be called from the request handler (/dev/loop).
@@ -325,6 +333,21 @@ cleaned, or an error value if not. Note that in order to prevent the page
getting mapped back in and redirtied, it needs to be kept locked
across the entire operation.
+ ->swap_activate will be called with a non-zero argument on
+files backing (non block device backed) swapfiles. A return value
+of zero indicates success, in which case this file can be used for
+backing swapspace. The swapspace operations will be proxied to the
+address space operations.
+
+ ->swap_deactivate() will be called in the sys_swapoff()
+path after ->swap_activate() returned success.
+
+ ->swap_writepage() is usable after swap_activate() returned
+success. This method is used to write a swap page.
+
+ ->swap_readpage() is usable after swap_activate() returned
+success, this method is used to read a swap page.
+
----------------------- file_lock_operations ------------------------------
prototypes:
void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 52d8fb8..8378eaa 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -581,6 +581,11 @@ struct address_space_operations {
int (*migratepage) (struct page *, struct page *);
int (*launder_page) (struct page *);
int (*error_remove_page) (struct mapping *mapping, struct page *page);
+ int (*swap_activate)(struct file *);
+ int (*swap_deactivate)(struct file *);
+ int (*swap_out)(struct file *, struct page *,
+ struct writeback_control *);
+ int (*swap_in)(struct file *, struct page *);
};
writepage: called by the VM to write a dirty page to backing store.
@@ -749,6 +754,22 @@ struct address_space_operations {
Setting this implies you deal with pages going away under you,
unless you have them locked or reference counts increased.
+ swap_activate: Called when swapon is used on a file to allocating
+ space if necessary and perform any other necessary
+ housekeeping. A return value of zero indicates success,
+ in which case this file can be used to back swapspace. The
+ swapspace operations will be proxied to this address space's
+ ->swap_{out,in} methods.
+
+ swap_deactivate: Called during swapoff on files where swap_activate
+ was successful.
+
+ swap_writepage: Called to write a swapcache page to a backing store,
+ similar to writepage.
+
+ swap_readpage: Called to read a swapcache page from a backing store,
+ similar to readpage.
+
The File Object
===============
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c2bd68f..387b767 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -617,6 +617,13 @@ struct address_space_operations {
int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
unsigned long);
int (*error_remove_page)(struct address_space *, struct page *);
+
+ /* swapfile support */
+ int (*swap_activate)(struct file *file);
+ int (*swap_deactivate)(struct file *file);
+ int (*swap_writepage)(struct file *file, struct page *page,
+ struct writeback_control *wbc);
+ int (*swap_readpage)(struct file *file, struct page *page);
};
extern const struct address_space_operations empty_aops;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 14d6249..a044198 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -148,6 +148,7 @@ enum {
SWP_SOLIDSTATE = (1 << 4), /* blkdev seeks are cheap */
SWP_CONTINUED = (1 << 5), /* swap_map has count continuation */
SWP_BLKDEV = (1 << 6), /* its a block device */
+ SWP_FILE = (1 << 7), /* set after swap_activate success */
/* add others here before... */
SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */
};
@@ -303,6 +304,7 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern int swap_set_page_dirty(struct page *page);
extern void end_swap_bio_read(struct bio *bio, int err);
/* linux/mm/swap_state.c */
@@ -339,6 +341,7 @@ extern int swap_type_of(dev_t, sector_t, struct block_device **);
extern unsigned int count_swap_pages(int, int);
extern sector_t map_swap_page(struct page *, struct block_device **);
extern sector_t swapdev_block(int, pgoff_t);
+extern struct swap_info_struct *page_swap_info(struct page *);
extern int reuse_swap_page(struct page *);
extern int try_to_free_swap(struct page *);
struct backing_dev_info;
diff --git a/mm/page_io.c b/mm/page_io.c
index dc76b4d..5ed5710 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -17,6 +17,7 @@
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/swapops.h>
+#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <asm/pgtable.h>
@@ -93,11 +94,23 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
{
struct bio *bio;
int ret = 0, rw = WRITE;
+ struct swap_info_struct *sis = page_swap_info(page);
if (try_to_free_swap(page)) {
unlock_page(page);
goto out;
}
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ ret = mapping->a_ops->swap_writepage(swap_file, page, wbc);
+ if (!ret)
+ count_vm_event(PSWPOUT);
+ return ret;
+ }
+
bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
if (bio == NULL) {
set_page_dirty(page);
@@ -119,9 +132,21 @@ int swap_readpage(struct page *page)
{
struct bio *bio;
int ret = 0;
+ struct swap_info_struct *sis = page_swap_info(page);
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(PageUptodate(page));
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ ret = mapping->a_ops->swap_readpage(swap_file, page);
+ if (!ret)
+ count_vm_event(PSWPIN);
+ return ret;
+ }
+
bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
if (bio == NULL) {
unlock_page(page);
@@ -133,3 +158,15 @@ int swap_readpage(struct page *page)
out:
return ret;
}
+
+int swap_set_page_dirty(struct page *page)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+
+ if (sis->flags & SWP_FILE) {
+ struct address_space *mapping = sis->swap_file->f_mapping;
+ return mapping->a_ops->set_page_dirty(page);
+ } else {
+ return __set_page_dirty_nobuffers(page);
+ }
+}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 4668046..787ca54 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -28,7 +28,7 @@
*/
static const struct address_space_operations swap_aops = {
.writepage = swap_writepage,
- .set_page_dirty = __set_page_dirty_nobuffers,
+ .set_page_dirty = swap_set_page_dirty,
.migratepage = migrate_page,
};
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 17bc224..f181884 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1343,6 +1343,14 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
list_del(&se->list);
kfree(se);
}
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ sis->flags &= ~SWP_FILE;
+ mapping->a_ops->swap_deactivate(swap_file);
+ }
}
/*
@@ -1424,7 +1432,9 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
*/
static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
{
- struct inode *inode;
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+ struct inode *inode = mapping->host;
unsigned blocks_per_page;
unsigned long page_no;
unsigned blkbits;
@@ -1435,13 +1445,22 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
int nr_extents = 0;
int ret;
- inode = sis->swap_file->f_mapping->host;
if (S_ISBLK(inode->i_mode)) {
ret = add_swap_extent(sis, 0, sis->max, 0);
*span = sis->pages;
goto out;
}
+ if (mapping->a_ops->swap_activate) {
+ ret = mapping->a_ops->swap_activate(swap_file);
+ if (!ret) {
+ sis->flags |= SWP_FILE;
+ ret = add_swap_extent(sis, 0, sis->max, 0);
+ *span = sis->pages;
+ }
+ goto out;
+ }
+
blkbits = inode->i_blkbits;
blocks_per_page = PAGE_SIZE >> blkbits;
@@ -2289,6 +2308,13 @@ int swapcache_prepare(swp_entry_t entry)
return __swap_duplicate(entry, SWAP_HAS_CACHE);
}
+struct swap_info_struct *page_swap_info(struct page *page)
+{
+ swp_entry_t swap = { .val = page_private(page) };
+ BUG_ON(!PageSwapCache(page));
+ return swap_info[swp_type(swap)];
+}
+
/*
* swap_lock prevents swap_map being freed. Don't grab an extra
* reference on the swaphandle, it doesn't matter if it becomes unused.
--
1.7.3.4
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