[RFC][PATCH -mm 0/2] Additional function in swapfile.c (needed for swap suspend)

[RFC][PATCH -mm 0/2] Additional function in swapfile.c (needed for swap suspend)

[Rafael J. Wysocki]

Hi,

To implement the image-writing part of swsusp in the user space and maintain
the compatibility with the in-kernel implementation we need to be able to
ask the kernel to allocate a swap page from specific swap partition.  For this
purpose we need a function allowing us to specify the swap partition to
allocate from.

Moreover, if we had such a function, we could change the in-kernel
implementation of swsusp to avoid locking of the swap devices that
are not used for suspend and this would allow us to simplify the code
quite a bit.

The first of the following two patches adds such a function, and the second
of them shows what can be done in swsusp if that function is available.

All of your comments and/or suggestions will be appreciated.

Greetings,
Rafael

[RFC][PATCH -mm 1/2] Additional function in swapfile.c (needed for swap suspend)

[Rafael J. Wysocki]

This patch adds the function get_swap_page_of_type() allowing us to
specify an index in swap_info[] and select a swap_info_struct
structure to be used for allocating a swap page.

This function (or another one of similar functionality) will be necessary for
implementing the image-writing part of swsusp in the user space.  It can also
be used for simplifying the current in-kernel implementation of the
image-writing part of swsusp.


Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

 include/linux/swap.h |    1 +
 mm/swapfile.c        |   20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

Index: linux-2.6.15-rc5-mm3/mm/swapfile.c
===================================================================
--- linux-2.6.15-rc5-mm3.orig/mm/swapfile.c	2005-12-15 12:01:39.000000000 +0100
+++ linux-2.6.15-rc5-mm3/mm/swapfile.c	2005-12-15 19:00:45.000000000 +0100
@@ -211,6 +211,26 @@
 	return (swp_entry_t) {0};
 }
 
+swp_entry_t get_swap_page_of_type(int type)
+{
+	struct swap_info_struct *si;
+	pgoff_t offset;
+
+	spin_lock(&swap_lock);
+	si = swap_info + type;
+	if (si->flags & SWP_WRITEOK) {
+		nr_swap_pages--;
+		offset = scan_swap_map(si);
+		if (offset) {
+			spin_unlock(&swap_lock);
+			return swp_entry(type, offset);
+		}
+		nr_swap_pages++;
+	}
+	spin_unlock(&swap_lock);
+	return (swp_entry_t) {0};
+}
+
 static struct swap_info_struct * swap_info_get(swp_entry_t entry)
 {
 	struct swap_info_struct * p;
Index: linux-2.6.15-rc5-mm3/include/linux/swap.h
===================================================================
--- linux-2.6.15-rc5-mm3.orig/include/linux/swap.h	2005-12-15 12:03:26.000000000 +0100
+++ linux-2.6.15-rc5-mm3/include/linux/swap.h	2005-12-15 19:00:46.000000000 +0100
@@ -216,6 +216,7 @@
 extern struct swap_info_struct swap_info[];
 extern void si_swapinfo(struct sysinfo *);
 extern swp_entry_t get_swap_page(void);
+extern swp_entry_t get_swap_page_of_type(int type);
 extern int swap_duplicate(swp_entry_t);
 extern int valid_swaphandles(swp_entry_t, unsigned long *);
 extern void swap_free(swp_entry_t);

[RFC][PATCH -mm 2/2] Additional function in swapfile.c (needed for swap suspend)

[Rafael J. Wysocki]

This patch contains the modification that can be made to swsusp once the
function defined in the previous patch has been introduced.


Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

 kernel/power/swsusp.c |   84 +++++++++++---------------------------------------
 1 files changed, 19 insertions(+), 65 deletions(-)

Index: linux-2.6.15-rc5-mm3/kernel/power/swsusp.c
===================================================================
--- linux-2.6.15-rc5-mm3.orig/kernel/power/swsusp.c	2005-12-15 22:49:49.000000000 +0100
+++ linux-2.6.15-rc5-mm3/kernel/power/swsusp.c	2005-12-15 22:50:01.000000000 +0100
@@ -104,13 +104,7 @@
  * Saving part...
  */
 
-/* We memorize in swapfile_used what swap devices are used for suspension */
-#define SWAPFILE_UNUSED    0
-#define SWAPFILE_SUSPEND   1	/* This is the suspending device */
-#define SWAPFILE_IGNORED   2	/* Those are other swap devices ignored for suspension */
-
-static unsigned short swapfile_used[MAX_SWAPFILES];
-static unsigned short root_swap;
+static unsigned short root_swap = 0xffff;
 
 static int mark_swapfiles(swp_entry_t prev)
 {
@@ -146,7 +140,7 @@
  * devfs, since the resume code can only recognize the form /dev/hda4,
  * but the suspend code would see the long name.)
  */
-static int is_resume_device(const struct swap_info_struct *swap_info)
+static inline int is_resume_device(const struct swap_info_struct *swap_info)
 {
 	struct file *file = swap_info->swap_file;
 	struct inode *inode = file->f_dentry->d_inode;
@@ -157,54 +151,22 @@
 
 static int swsusp_swap_check(void) /* This is called before saving image */
 {
-	int i, len;
-
-	len=strlen(resume_file);
-	root_swap = 0xFFFF;
-
-	spin_lock(&swap_lock);
-	for (i=0; i<MAX_SWAPFILES; i++) {
-		if (!(swap_info[i].flags & SWP_WRITEOK)) {
-			swapfile_used[i]=SWAPFILE_UNUSED;
-		} else {
-			if (!len) {
-	    			printk(KERN_WARNING "resume= option should be used to set suspend device" );
-				if (root_swap == 0xFFFF) {
-					swapfile_used[i] = SWAPFILE_SUSPEND;
-					root_swap = i;
-				} else
-					swapfile_used[i] = SWAPFILE_IGNORED;
-			} else {
-	  			/* we ignore all swap devices that are not the resume_file */
-				if (is_resume_device(&swap_info[i])) {
-					swapfile_used[i] = SWAPFILE_SUSPEND;
-					root_swap = i;
-				} else {
-				  	swapfile_used[i] = SWAPFILE_IGNORED;
-				}
-			}
-		}
-	}
-	spin_unlock(&swap_lock);
-	return (root_swap != 0xffff) ? 0 : -ENODEV;
-}
-
-/**
- * This is called after saving image so modification
- * will be lost after resume... and that's what we want.
- * we make the device unusable. A new call to
- * lock_swapdevices can unlock the devices.
- */
-static void lock_swapdevices(void)
-{
 	int i;
 
+	if (!swsusp_resume_device)
+		return -ENODEV;
 	spin_lock(&swap_lock);
-	for (i = 0; i< MAX_SWAPFILES; i++)
-		if (swapfile_used[i] == SWAPFILE_IGNORED) {
-			swap_info[i].flags ^= SWP_WRITEOK;
+	for (i = 0; i < MAX_SWAPFILES; i++) {
+		if (!(swap_info[i].flags & SWP_WRITEOK))
+			continue;
+		if (is_resume_device(swap_info + i)) {
+			spin_unlock(&swap_lock);
+			root_swap = i;
+			return 0;
 		}
+	}
 	spin_unlock(&swap_lock);
+	return -ENODEV;
 }
 
 /**
@@ -222,19 +184,14 @@
 static int write_page(unsigned long addr, swp_entry_t *loc)
 {
 	swp_entry_t entry;
-	int error = 0;
+	int error = -ENOSPC;
 
-	entry = get_swap_page();
-	if (swp_offset(entry) &&
-	    swapfile_used[swp_type(entry)] == SWAPFILE_SUSPEND) {
-		error = rw_swap_page_sync(WRITE, entry,
-					  virt_to_page(addr));
-		if (error == -EIO)
-			error = 0;
-		if (!error)
+	entry = get_swap_page_of_type(root_swap);
+	if (swp_offset(entry)) {
+		error = rw_swap_page_sync(WRITE, entry, virt_to_page(addr));
+		if (!error || error == -EIO)
 			*loc = entry;
-	} else
-		error = -ENOSPC;
+	}
 	return error;
 }
 
@@ -614,10 +571,7 @@
 		printk(KERN_ERR "swsusp: cannot find swap device, try swapon -a.\n");
 		return error;
 	}
-	lock_swapdevices();
 	error = write_suspend_image(pblist, nr_pages);
-	/* This will unlock ignored swap devices since writing is finished */
-	lock_swapdevices();
 	return error;
 }