[PATCH 576/577] swap: Add swap slot free callback to block_device_operations

Greg Kroah-Hartman gregkh at suse.de
Fri May 21 20:05:05 UTC 2010


From: Nitin Gupta <ngupta at vflare.org>

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 <ngupta at vflare.org>
Acked-by: Linus Torvalds <torvalds at linux-foundation.org>
Acked-by: Nigel Cunningham <nigel at tuxonice.net>
Acked-by: Pekka Enberg <penberg at cs.helsinki.fi>
Reviewed-by: Minchan Kim <minchan.kim at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
---
 include/linux/blkdev.h |    2 ++
 mm/swapfile.c          |    4 ++++
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6690e8b..413284a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1287,6 +1287,8 @@ 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/mm/swapfile.c b/mm/swapfile.c
index ecb069e..f5ccc47 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -574,6 +574,7 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
 
 	/* free if no reference */
 	if (!usage) {
+		struct gendisk *disk = p->bdev->bd_disk;
 		if (offset < p->lowest_bit)
 			p->lowest_bit = offset;
 		if (offset > p->highest_bit)
@@ -583,6 +584,9 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
 			swap_list.next = p->type;
 		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);
 	}
 
 	return usage;
-- 
1.7.0.3




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