Messages in this thread Patch in this message | | | Date | Tue, 19 Oct 2010 16:38:37 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] support polling of /proc/swaps |
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On Wed, 20 Oct 2010 01:25:47 +0200 Kay Sievers <kay.sievers@vrfy.org> wrote:
> On Tue, 2010-10-19 at 15:31 -0700, Andrew Morton wrote: > > On Tue, 19 Oct 2010 11:19:16 +0200 > > Kay Sievers <kay.sievers@vrfy.org> wrote: > > > It's a bit sad that we have to add quite a pile of infrastructure to > > make a procfs file pollable. I wonder if it's possible to provide some > > core support for this, and reduce the amount of code at each particular > > handler site. > > You mean something like adding the event counter to the seq_file? There > is /proc/self/mounts,mountinfo and /proc/swaps so far, I think.
Don't know - I was just waving hands about wondering if we really need to add 48 new lines of code each time we want to make a procfs file pollable.
> > Also, I wonder how we are to communicate the existence of this feature > > to our users. Nobody will look in Documentation/filesystems/. Is > > there a manpage? Seems not... > > Hmm, 'man 5 proc'?
yes, that mentions /proc/swaps.
> > > +static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); > > > +static int proc_poll_event; > > > > Please pick a lock to protect proc_poll_event. > > An atomic_t should do it too, right?
It does.
> > Then document that > > locking here, when you also document proc_poll_event ;) > > The actual value has no meaning at all, it just tells that something > happened if it has changed. >
bah.
--- a/mm/swapfile.c~proc-swaps-support-polling-fix +++ a/mm/swapfile.c @@ -60,6 +60,7 @@ static struct swap_info_struct *swap_inf static DEFINE_MUTEX(swapon_mutex); static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); +/* Activity counter to indicate that a swapon or swapoff has occurred */ static atomic_t proc_poll_event = ATOMIC_INIT(0); static inline unsigned char swap_count(unsigned char ent) _
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