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Subject[PATCH 03/20] mm: add support for non block device backed swap files
Date
From
A new addres_space_operations method is added:
int swapfile(struct address_space *, int)

When during sys_swapon() this method is found and returns no error the
swapper_space.a_ops will proxy to sis->swap_file->f_mapping->a_ops.

The swapfile method will be used to communicate to the address_space that the
VM relies on it, and the address_space should take adequate measures (like
reserving memory for mempools or the like).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Trond Myklebust <trond.myklebust@fys.uio.no>
---
fs/buffer.c | 2 -
include/linux/fs.h | 1
include/linux/swap.h | 4 +++
init/Kconfig | 5 ++++
mm/page_io.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++
mm/swap_state.c | 6 +++++
mm/swapfile.c | 27 ++++++++++++++++++++++
7 files changed, 103 insertions(+), 2 deletions(-)
Index: linux-2.6/include/linux/swap.h
===================================================================
--- linux-2.6.orig/include/linux/swap.h
+++ linux-2.6/include/linux/swap.h
@@ -115,6 +115,7 @@ enum {
SWP_USED = (1 << 0), /* is slot in swap_info[] used? */
SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */
SWP_ACTIVE = (SWP_USED | SWP_WRITEOK),
+ SWP_FILE = (1 << 2), /* file swap area */
/* add others here before... */
SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */
};
@@ -212,6 +213,9 @@ extern void swap_unplug_io_fn(struct bac
/* linux/mm/page_io.c */
extern int swap_readpage(struct file *, struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern void swap_sync_page(struct page *page);
+extern int swap_set_page_dirty(struct page *page);
+extern int swap_releasepage(struct page *page, gfp_t gfp_mask);
extern int rw_swap_page_sync(int, swp_entry_t, struct page *);

/* linux/mm/swap_state.c */
Index: linux-2.6/init/Kconfig
===================================================================
--- linux-2.6.orig/init/Kconfig
+++ linux-2.6/init/Kconfig
@@ -100,6 +100,11 @@ config SWAP
used to provide more virtual memory than the actual RAM present
in your computer. If unsure say Y.

+config SWAP_FILE
+ bool "Support for paging to/from non block device files"
+ depends on SWAP
+ default n
+
config SYSVIPC
bool "System V IPC"
---help---
Index: linux-2.6/mm/page_io.c
===================================================================
--- linux-2.6.orig/mm/page_io.c
+++ linux-2.6/mm/page_io.c
@@ -17,6 +17,7 @@
#include <linux/bio.h>
#include <linux/swapops.h>
#include <linux/writeback.h>
+#include <linux/buffer_head.h>
#include <asm/pgtable.h>

static struct bio *get_swap_bio(gfp_t gfp_flags, pgoff_t index,
@@ -91,6 +92,14 @@ int swap_writepage(struct page *page, st
unlock_page(page);
goto out;
}
+#ifdef CONFIG_SWAP_FILE
+ {
+ struct swap_info_struct *sis = page_swap_info(page);
+ if (sis->flags & SWP_FILE)
+ return sis->swap_file->f_mapping->
+ a_ops->writepage(page, wbc);
+ }
+#endif
bio = get_swap_bio(GFP_NOIO, page_private(page), page,
end_swap_bio_write);
if (bio == NULL) {
@@ -116,6 +125,14 @@ int swap_readpage(struct file *file, str

BUG_ON(!PageLocked(page));
ClearPageUptodate(page);
+#ifdef CONFIG_SWAP_FILE
+ {
+ struct swap_info_struct *sis = page_swap_info(page);
+ if (sis->flags & SWP_FILE)
+ return sis->swap_file->f_mapping->
+ a_ops->readpage(sis->swap_file, page);
+ }
+#endif
bio = get_swap_bio(GFP_KERNEL, page_private(page), page,
end_swap_bio_read);
if (bio == NULL) {
@@ -129,6 +146,49 @@ out:
return ret;
}

+#ifdef CONFIG_SWAP_FILE
+void swap_sync_page(struct page *page)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+
+ if (sis->flags & SWP_FILE) {
+ const struct address_space_operations * a_ops =
+ sis->swap_file->f_mapping->a_ops;
+ if (a_ops->sync_page)
+ a_ops->sync_page(page);
+ } else
+ block_sync_page(page);
+}
+
+int swap_set_page_dirty(struct page *page)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+
+ if (sis->flags & SWP_FILE) {
+ const struct address_space_operations * a_ops =
+ sis->swap_file->f_mapping->a_ops;
+ if (a_ops->set_page_dirty)
+ return a_ops->set_page_dirty(page);
+ return __set_page_dirty_buffers(page);
+ }
+
+ return __set_page_dirty_nobuffers(page);
+}
+
+int swap_releasepage(struct page *page, gfp_t gfp_mask)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+ const struct address_space_operations * a_ops =
+ sis->swap_file->f_mapping->a_ops;
+
+ if ((sis->flags & SWP_FILE) && a_ops->releasepage)
+ return a_ops->releasepage(page, gfp_mask);
+
+ BUG();
+ return 0;
+}
+#endif
+
#ifdef CONFIG_SOFTWARE_SUSPEND
/*
* A scruffy utility function to read or write an arbitrary swap page
Index: linux-2.6/mm/swap_state.c
===================================================================
--- linux-2.6.orig/mm/swap_state.c
+++ linux-2.6/mm/swap_state.c
@@ -26,8 +26,14 @@
*/
static const struct address_space_operations swap_aops = {
.writepage = swap_writepage,
+#ifdef CONFIG_SWAP_FILE
+ .sync_page = swap_sync_page,
+ .set_page_dirty = swap_set_page_dirty,
+ .releasepage = swap_releasepage,
+#else
.sync_page = block_sync_page,
.set_page_dirty = __set_page_dirty_nobuffers,
+#endif
.migratepage = migrate_page,
};

Index: linux-2.6/mm/swapfile.c
===================================================================
--- linux-2.6.orig/mm/swapfile.c
+++ linux-2.6/mm/swapfile.c
@@ -411,7 +411,12 @@ void free_swap_and_cache(swp_entry_t ent
if (page) {
int one_user;

+#ifdef CONFIG_SWAP_FILE
+ if (PagePrivate(page))
+ page_mapping(page)->a_ops->releasepage(page, 0);
+#else
BUG_ON(PagePrivate(page));
+#endif
one_user = (page_count(page) == 2);
/* Only cache user (+us), or swap space full? Free it! */
/* Also recheck PageSwapCache after page is locked (above) */
@@ -944,6 +949,13 @@ static void destroy_swap_extents(struct
list_del(&se->list);
kfree(se);
}
+#ifdef CONFIG_SWAP_FILE
+ if (sis->flags & SWP_FILE) {
+ sis->flags &= ~SWP_FILE;
+ sis->swap_file->f_mapping->a_ops->
+ swapfile(sis->swap_file->f_mapping, 0);
+ }
+#endif
}

/*
@@ -1036,6 +1048,19 @@ static int setup_swap_extents(struct swa
goto done;
}

+#ifdef CONFIG_SWAP_FILE
+ if (sis->swap_file->f_mapping->a_ops->swapfile) {
+ ret = sis->swap_file->f_mapping->a_ops->
+ swapfile(sis->swap_file->f_mapping, 1);
+ if (!ret) {
+ sis->flags |= SWP_FILE;
+ ret = add_swap_extent(sis, 0, sis->max, 0);
+ *span = sis->pages;
+ }
+ goto done;
+ }
+#endif
+
blkbits = inode->i_blkbits;
blocks_per_page = PAGE_SIZE >> blkbits;

@@ -1592,7 +1617,7 @@ asmlinkage long sys_swapon(const char __

mutex_lock(&swapon_mutex);
spin_lock(&swap_lock);
- p->flags = SWP_ACTIVE;
+ p->flags |= SWP_WRITEOK;
nr_swap_pages += nr_good_pages;
total_swap_pages += nr_good_pages;

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -382,6 +382,7 @@ struct address_space_operations {
/* migrate the contents of a page to the specified target */
int (*migratepage) (struct address_space *,
struct page *, struct page *);
+ int (*swapfile)(struct address_space *, int);
};

struct backing_dev_info;
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -1567,7 +1567,7 @@ static void discard_buffer(struct buffer
*/
int try_to_release_page(struct page *page, gfp_t gfp_mask)
{
- struct address_space * const mapping = page->mapping;
+ struct address_space * const mapping = page_mapping(page);

BUG_ON(!PageLocked(page));
if (PageWriteback(page))
--

-
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