Messages in this thread | | | Date | Thu, 14 Jan 2010 15:10:14 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [PATCH] [mmotm] comment on swap notify locking constraints |
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On Thu, 14 Jan 2010, Nitin Gupta wrote:
> A block device makes swap_slot_free_notify() callback > when the last reference to a swap slot is dropped. > > This callback is made under swap_lock and often with > lock for corresponding swapcache page also held. This > is a note of warning for registered callback function > which must meet these constraints.
You're right that the page lock of the corresponding swapcache page may be held there, but that isn't what worried me enough to ask for a comment: it's the page table lock (sometimes we call it pte lock), a spinlock like the swap_lock, being held there that particularly deserves comment. We don't want someone going to lots of effort to avoid holding swap_lock there, only to find that effort wasted because page table lock is also held.
Hugh
> > Signed-off-by: Nitin Gupta <ngupta@vflare.org> > --- > include/linux/blkdev.h | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index 14b95a3..e3dcff6 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 *); > + /* this callback is with swap_lock and often page lock also held */
and page table lock
> void (*swap_slot_free_notify) (struct block_device *, unsigned long); > struct module *owner; > }; > -- > 1.6.2.5
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