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Message-ID: <7bb897f31fded59aae8d62a6796dd21feebd0642.camel@kernel.org>
Date: Mon, 15 Jul 2024 15:53:42 -0400
From: Jeff Layton <jlayton@...nel.org>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
<brauner@...nel.org>, Jan Kara <jack@...e.cz>, Steven Rostedt
<rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu
Desnoyers <mathieu.desnoyers@...icios.com>, Chandan Babu R
<chandan.babu@...cle.com>, Theodore Ts'o <tytso@....edu>, Andreas Dilger
<adilger.kernel@...ger.ca>, Chris Mason <clm@...com>, Josef Bacik
<josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Hugh Dickins
<hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Jonathan
Corbet <corbet@....net>, Dave Chinner <david@...morbit.com>, Andi Kleen
<ak@...ux.intel.com>, Christoph Hellwig <hch@...radead.org>, Uros Bizjak
<ubizjak@...il.com>, Kent Overstreet <kent.overstreet@...ux.dev>, Arnd
Bergmann <arnd@...db.de>, Randy Dunlap <rdunlap@...radead.org>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
linux-mm@...ck.org, linux-nfs@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 3/9] fs: add percpu counters for significant
multigrain timestamp events
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@...icpanda.com>
> > Signed-off-by: Jeff Layton <jlayton@...nel.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@...nel.org>
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