Messages in this thread | | | Date | Fri, 07 May 2010 19:22:30 +1000 | From | Nigel Cunningham <> | Subject | Re: [PATCH 2/3] Add swap slot free callback to block_device_operations |
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Hi.
On 07/05/10 17:25, Nitin Gupta wrote: > 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@vflare.org> > --- > 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);
Is this p->flags & SWP_BLKDEV logic reversed? (Don't you want the notifier called for devices that aren't backed by a block device?)
I also wonder whether leaving the p->flags & SWP_BLKDEV part out might be a good idea. Other potential notifier users?
Regards,
Nigel
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