swap: Add swap slot free callback to block_device_operations

This callback is required when RAM based devices are used as swap disks. One such device is ramzswap which is used as compressed in-memory swap disk. For such devices, we need a callback as soon as a swap slot is no longer used to allow freeing memory allocated for this slot. Without this callback, stale data can quickly accumulate in memory defeating the whole purpose of such devices. Signed-off-by: Nitin Gupta <[email protected]> Acked-by: Linus Torvalds <[email protected]> Acked-by: Nigel Cunningham <[email protected]> Acked-by: Pekka Enberg <[email protected]> Reviewed-by: Minchan Kim <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
cybik · Nov 2, 2011 · be24287 · be24287
1 parent 14d2122
commit be24287
Show file tree

Hide file tree

Showing 3 changed files with 8 additions and 0 deletions.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
@@ -1288,6 +1288,8 @@ struct block_device_operations {
 						unsigned long long);
 	int (*revalidate_disk) (struct gendisk *);
 	int (*getgeo)(struct block_device *, struct hd_geometry *);
+	/* this callback is with swap_lock and sometimes page table lock held */
+	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
 	struct module *owner;
 };
 

diff --git a/include/linux/swap.h b/include/linux/swap.h
@@ -145,6 +145,7 @@ enum {
 	SWP_DISCARDABLE = (1 << 2),	/* blkdev supports discard */
 	SWP_DISCARDING	= (1 << 3),	/* now discarding a free cluster */
 	SWP_SOLIDSTATE	= (1 << 4),	/* blkdev seeks are cheap */
+	SWP_BLKDEV      = (1 << 6),     /* its a block device */
 					/* add others here before... */
 	SWP_SCANNING	= (1 << 8),	/* refcount in scan_swap_map */
 };

diff --git a/mm/swapfile.c b/mm/swapfile.c
@@ -579,6 +579,7 @@ static int swap_entry_free(struct swap_info_struct *p,
 	count = p->swap_map[offset];
 	/* free if no reference */
 	if (!count) {
+		struct gendisk *disk = p->bdev->bd_disk;
 		if (offset < p->lowest_bit)
 			p->lowest_bit = offset;
 		if (offset > p->highest_bit)
@@ -587,6 +588,9 @@ static int swap_entry_free(struct swap_info_struct *p,
 			swap_list.next = p - swap_info;
 		nr_swap_pages++;
 		p->inuse_pages--;
+		if ((p->flags & SWP_BLKDEV) &&
+			disk->fops->swap_slot_free_notify)
+			disk->fops->swap_slot_free_notify(p->bdev, offset);
 	}
 	if (!swap_count(count))
 		mem_cgroup_uncharge_swap(ent);
@@ -1877,6 +1881,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		if (error < 0)
 			goto bad_swap;
 		p->bdev = bdev;
+		p->flags |= SWP_BLKDEV;
 	} else if (S_ISREG(inode->i_mode)) {
 		p->bdev = inode->i_sb->s_bdev;
 		mutex_lock(&inode->i_mutex);