Messages in this thread |  | | | Date | Fri, 07 May 2010 15:18:56 +0530 | | From | Nitin Gupta <> | | Subject | Re: [PATCH 2/3] Add swap slot free callback to block_device_operations |
| |
On 05/07/2010 02:52 PM, Nigel Cunningham wrote: > 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?) >
No, the logic here is correct: ramzswap is a block device for which we want this callback. Though its a RAM backed, it is still a block device.
(I hope it answers your question in the other mail also).
> I also wonder whether leaving the p->flags & SWP_BLKDEV part out might > be a good idea. Other potential notifier users? >
For regular files, 'offset' used here makes little sense. For block devices, its simply offset in real device. Also, I doubt if *files* would ever like to have such a callback.
Thanks, Nitin
|  |