Re: [PATCH v6 3/9] fs: add percpu counters for significant multigrain timestamp events

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2024-07-15 at 11:32 -0700, Darrick J. Wong wrote:
> On Mon, Jul 15, 2024 at 08:48:54AM -0400, Jeff Layton wrote:
> > Four percpu counters for counting various stats around mgtimes, and
> > a
> > new debugfs file for displaying them:
> > 
> > - number of attempted ctime updates
> > - number of successful i_ctime_nsec swaps
> > - number of fine-grained timestamp fetches
> > - number of floor value swaps
> > 
> > Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/inode.c | 70
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 69 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 869994285e87..fff844345c35 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -21,6 +21,8 @@
> >  #include <linux/list_lru.h>
> >  #include <linux/iversion.h>
> >  #include <linux/rw_hint.h>
> > +#include <linux/seq_file.h>
> > +#include <linux/debugfs.h>
> >  #include <trace/events/writeback.h>
> >  #define CREATE_TRACE_POINTS
> >  #include <trace/events/timestamp.h>
> > @@ -80,6 +82,10 @@ EXPORT_SYMBOL(empty_aops);
> >  
> >  static DEFINE_PER_CPU(unsigned long, nr_inodes);
> >  static DEFINE_PER_CPU(unsigned long, nr_unused);
> > +static DEFINE_PER_CPU(unsigned long, mg_ctime_updates);
> > +static DEFINE_PER_CPU(unsigned long, mg_fine_stamps);
> > +static DEFINE_PER_CPU(unsigned long, mg_floor_swaps);
> > +static DEFINE_PER_CPU(unsigned long, mg_ctime_swaps);
> 
> Should this all get switched off if CONFIG_DEBUG_FS=n?
> 
> --D
> 

Sure, why not. That's simple enough to do.

I pushed an updated mgtime branch to my git tree. Here's the updated
patch that's the only difference:

    https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/commit/?h=mgtime&id=ee7fe6e9c0598754861c8620230f15f3de538ca5

Seems to build OK both with and without CONFIG_DEBUG_FS.
 
> >  
> >  static struct kmem_cache *inode_cachep __ro_after_init;
> >  
> > @@ -101,6 +107,42 @@ static inline long get_nr_inodes_unused(void)
> >  	return sum < 0 ? 0 : sum;
> >  }
> >  
> > +static long get_mg_ctime_updates(void)
> > +{
> > +	int i;
> > +	long sum = 0;
> > +	for_each_possible_cpu(i)
> > +		sum += per_cpu(mg_ctime_updates, i);
> > +	return sum < 0 ? 0 : sum;
> > +}
> > +
> > +static long get_mg_fine_stamps(void)
> > +{
> > +	int i;
> > +	long sum = 0;
> > +	for_each_possible_cpu(i)
> > +		sum += per_cpu(mg_fine_stamps, i);
> > +	return sum < 0 ? 0 : sum;
> > +}
> > +
> > +static long get_mg_floor_swaps(void)
> > +{
> > +	int i;
> > +	long sum = 0;
> > +	for_each_possible_cpu(i)
> > +		sum += per_cpu(mg_floor_swaps, i);
> > +	return sum < 0 ? 0 : sum;
> > +}
> > +
> > +static long get_mg_ctime_swaps(void)
> > +{
> > +	int i;
> > +	long sum = 0;
> > +	for_each_possible_cpu(i)
> > +		sum += per_cpu(mg_ctime_swaps, i);
> > +	return sum < 0 ? 0 : sum;
> > +}
> > +
> >  long get_nr_dirty_inodes(void)
> >  {
> >  	/* not actually dirty inodes, but a wild approximation */
> > @@ -2655,6 +2697,7 @@ struct timespec64
> > inode_set_ctime_current(struct inode *inode)
> >  
> >  			/* Get a fine-grained time */
> >  			fine = ktime_get();
> > +			this_cpu_inc(mg_fine_stamps);
> >  
> >  			/*
> >  			 * If the cmpxchg works, we take the new
> > floor value. If
> > @@ -2663,11 +2706,14 @@ struct timespec64
> > inode_set_ctime_current(struct inode *inode)
> >  			 * as good, so keep it.
> >  			 */
> >  			old = floor;
> > -			if (!atomic64_try_cmpxchg(&ctime_floor,
> > &old, fine))
> > +			if (atomic64_try_cmpxchg(&ctime_floor,
> > &old, fine))
> > +				this_cpu_inc(mg_floor_swaps);
> > +			else
> >  				fine = old;
> >  			now = ktime_mono_to_real(fine);
> >  		}
> >  	}
> > +	this_cpu_inc(mg_ctime_updates);
> >  	now_ts = timestamp_truncate(ktime_to_timespec64(now),
> > inode);
> >  	cur = cns;
> >  
> > @@ -2682,6 +2728,7 @@ struct timespec64
> > inode_set_ctime_current(struct inode *inode)
> >  		/* If swap occurred, then we're (mostly) done */
> >  		inode->i_ctime_sec = now_ts.tv_sec;
> >  		trace_ctime_ns_xchg(inode, cns, now_ts.tv_nsec,
> > cur);
> > +		this_cpu_inc(mg_ctime_swaps);
> >  	} else {
> >  		/*
> >  		 * Was the change due to someone marking the old
> > ctime QUERIED?
> > @@ -2751,3 +2798,24 @@ umode_t mode_strip_sgid(struct mnt_idmap
> > *idmap,
> >  	return mode & ~S_ISGID;
> >  }
> >  EXPORT_SYMBOL(mode_strip_sgid);
> > +
> > +static int mgts_show(struct seq_file *s, void *p)
> > +{
> > +	long ctime_updates = get_mg_ctime_updates();
> > +	long ctime_swaps = get_mg_ctime_swaps();
> > +	long fine_stamps = get_mg_fine_stamps();
> > +	long floor_swaps = get_mg_floor_swaps();
> > +
> > +	seq_printf(s, "%lu %lu %lu %lu\n",
> > +		   ctime_updates, ctime_swaps, fine_stamps,
> > floor_swaps);
> > +	return 0;
> > +}
> > +
> > +DEFINE_SHOW_ATTRIBUTE(mgts);
> > +
> > +static int __init mg_debugfs_init(void)
> > +{
> > +	debugfs_create_file("multigrain_timestamps", S_IFREG |
> > S_IRUGO, NULL, NULL, &mgts_fops);
> > +	return 0;
> > +}
> > +late_initcall(mg_debugfs_init);
> > 
> > -- 
> > 2.45.2
> > 
> > 

-- 
Jeff Layton <jlayton@kernel.org>