Messages in this thread |  | | | Date | Tue, 5 Jan 2010 10:58:00 +0000 (GMT) | | From | Hugh Dickins <> | | Subject | Re: [PATCH 1/2] [mmotm] Add swap slot free callback to block_device_operations |
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On Tue, 5 Jan 2010, Nitin Gupta wrote:
> This callback is required when RAM based devices are > used as swap disks. One such device is ramzswap[1] 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. > > Another user of this callback will be "preswap" as > introduced by "Transcendent Memory" patches: > http://lwn.net/Articles/367286/ > (I intend to integrade preswap with ramzswap). > > [1] ramzswap: http://code.google.com/p/compcache/ > > Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Yes, thanks for your patience in putting this together: I much prefer this version to all the other ways considered.
(Though you should later add a comment, pointing out that this callback is with swap_lock and often page table lock also held.)
We know that's unsatisfactory, but it is the nature of swap: cutting some corners to get the job done without allocating more memory. Having tried myself to do proper discard at swap_free time, I know that is hard: and I believe you've made the right decision to do it in this way for ramzswap.
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> --- > include/linux/blkdev.h | 1 + > mm/swapfile.c | 3 +++ > 2 files changed, 4 insertions(+), 0 deletions(-) > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index 784a919..14b95a3 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -1295,6 +1295,7 @@ struct block_device_operations { > unsigned long long); > int (*revalidate_disk) (struct gendisk *); > int (*getgeo)(struct block_device *, struct hd_geometry *); > + void (*swap_slot_free_notify) (struct block_device *, unsigned long); > struct module *owner; > }; > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 6c0585b..0c373bc 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 +584,8 @@ static unsigned char swap_entry_free(struct swap_info_struct *p, > swap_list.next = p->type; > nr_swap_pages++; > p->inuse_pages--; > + if (disk->fops->swap_slot_free_notify) > + disk->fops->swap_slot_free_notify(p->bdev, offset); > } > > return usage; > -- > 1.6.2.5
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