From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH v2 03/28] dcache: convert dentry_stat.nr_unused to per-cpu counters Date: Fri, 5 Apr 2013 12:15:06 +1100 Message-ID: <20130405011506.GG12011@dastard> References: <1364548450-28254-1-git-send-email-glommer@parallels.com> <1364548450-28254-4-git-send-email-glommer@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Dave Chinner , hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, Michal Hocko , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Johannes Weiner , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton To: Greg Thelen Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Apr 04, 2013 at 06:09:31PM -0700, Greg Thelen wrote: > On Fri, Mar 29 2013, Glauber Costa wrote: > > > From: Dave Chinner > > > > 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 > > Reviewed-by: Christoph Hellwig > > --- > > 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-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org