On Thu, Apr 04, 2013 at 06:09:31PM -0700, Greg Thelen wrote:
> On Fri, Mar 29 2013, Glauber Costa wrote:
>
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > Before we split up the dcache_lru_lock, the unused dentry counter
> > needs to be made independent of the global dcache_lru_lock. Convert
> > it to per-cpu counters to do this.
> >
> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > ---
> > fs/dcache.c | 17 ++++++++++++++---
> > 1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index fbfae008..f1196f2 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -118,6 +118,7 @@ struct dentry_stat_t dentry_stat = {
> > };
> >
> > static DEFINE_PER_CPU(unsigned int, nr_dentry);
> > +static DEFINE_PER_CPU(unsigned int, nr_dentry_unused);
> >
> > #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
> > static int get_nr_dentry(void)
> > @@ -129,10 +130,20 @@ static int get_nr_dentry(void)
> > return sum < 0 ? 0 : sum;
> > }
> >
> > +static int get_nr_dentry_unused(void)
> > +{
> > + int i;
> > + int sum = 0;
> > + for_each_possible_cpu(i)
> > + sum += per_cpu(nr_dentry_unused, i);
> > + return sum < 0 ? 0 : sum;
> > +}
>
> Just checking... If cpu x is removed, then its per cpu nr_dentry_unused
> count survives so we don't leak nr_dentry_unused. Right? I see code in
> percpu_counter_sum_positive() to explicitly handle this case and I want
> to make sure we don't need it here.
DEFINE_PER_CPU() gives a variable per possible CPU, and we sum for
all possible CPUs. Therefore online/offline CPUs just don't matter.
The percpu_counter code uses for_each_online_cpu(), and so it has to
be aware of hotplug operations so taht it doesn't leak counts.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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