[PATCH 10/19] netfs: Trace refcounting on the netfs_io_subrequest struct

From: David Howells
Date: Wed Mar 02 2022 - 09:07:50 EST

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Add refcount tracing for the netfs_io_subrequest structure.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---

fs/netfs/internal.h | 2 --
fs/netfs/objects.c | 26 ++++++++++++++++++++------
fs/netfs/read_helper.c | 20 +++++++++++---------
include/linux/netfs.h | 8 +++++++-
include/trace/events/netfs.h | 40 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 78 insertions(+), 18 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index b3877e276a3a..ee2f64cde221 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -27,8 +27,6 @@ void netfs_clear_subrequests(struct netfs_io_request *rreq, bool was_async);
void netfs_put_request(struct netfs_io_request *rreq, bool was_async,
enum netfs_rreq_ref_trace what);
struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq);
-void netfs_put_subrequest(struct netfs_io_subrequest *subreq, bool was_async);
-void netfs_get_subrequest(struct netfs_io_subrequest *subreq);

static inline void netfs_see_request(struct netfs_io_request *rreq,
enum netfs_rreq_ref_trace what)
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 57d53f1f6741..c46d027c1692 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -59,7 +59,8 @@ void netfs_clear_subrequests(struct netfs_io_request *rreq, bool was_async)
subreq = list_first_entry(&rreq->subrequests,
struct netfs_io_subrequest, rreq_link);
list_del(&subreq->rreq_link);
- netfs_put_subrequest(subreq, was_async);
+ netfs_put_subrequest(subreq, was_async,
+ netfs_sreq_trace_put_clear);
}
}

@@ -107,7 +108,7 @@ struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq
subreq = kzalloc(sizeof(struct netfs_io_subrequest), GFP_KERNEL);
if (subreq) {
INIT_LIST_HEAD(&subreq->rreq_link);
- refcount_set(&subreq->usage, 2);
+ refcount_set(&subreq->ref, 2);
subreq->rreq = rreq;
netfs_get_request(rreq, netfs_rreq_trace_get_subreq);
netfs_stat(&netfs_n_rh_sreq);
@@ -116,9 +117,14 @@ struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq
return subreq;
}

-void netfs_get_subrequest(struct netfs_io_subrequest *subreq)
+void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
+ enum netfs_sreq_ref_trace what)
{
- refcount_inc(&subreq->usage);
+ int r;
+
+ __refcount_inc(&subreq->ref, &r);
+ trace_netfs_sreq_ref(subreq->rreq->debug_id, subreq->debug_index, r + 1,
+ what);
}

static void netfs_free_subrequest(struct netfs_io_subrequest *subreq,
@@ -132,8 +138,16 @@ static void netfs_free_subrequest(struct netfs_io_subrequest *subreq,
netfs_put_request(rreq, was_async, netfs_rreq_trace_put_subreq);
}

-void netfs_put_subrequest(struct netfs_io_subrequest *subreq, bool was_async)
+void netfs_put_subrequest(struct netfs_io_subrequest *subreq, bool was_async,
+ enum netfs_sreq_ref_trace what)
{
- if (refcount_dec_and_test(&subreq->usage))
+ unsigned int debug_index = subreq->debug_index;
+ unsigned int debug_id = subreq->rreq->debug_id;
+ bool dead;
+ int r;
+
+ dead = __refcount_dec_and_test(&subreq->ref, &r);
+ trace_netfs_sreq_ref(debug_id, debug_index, r - 1, what);
+ if (dead)
netfs_free_subrequest(subreq, was_async);
}
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 535b2cbde4c8..c953a573b6b6 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -166,7 +166,7 @@ static void netfs_rreq_copy_terminated(void *priv, ssize_t transferred_or_error,
if (atomic_dec_and_test(&rreq->nr_copy_ops))
netfs_rreq_unmark_after_write(rreq, was_async);

- netfs_put_subrequest(subreq, was_async);
+ netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
}

/*
@@ -190,7 +190,8 @@ static void netfs_rreq_do_write_to_cache(struct netfs_io_request *rreq)
list_for_each_entry_safe(subreq, p, &rreq->subrequests, rreq_link) {
if (!test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
list_del_init(&subreq->rreq_link);
- netfs_put_subrequest(subreq, false);
+ netfs_put_subrequest(subreq, false,
+ netfs_sreq_trace_put_no_copy);
}
}

@@ -202,7 +203,8 @@ static void netfs_rreq_do_write_to_cache(struct netfs_io_request *rreq)
break;
subreq->len += next->len;
list_del_init(&next->rreq_link);
- netfs_put_subrequest(next, false);
+ netfs_put_subrequest(next, false,
+ netfs_sreq_trace_put_merged);
}

ret = cres->ops->prepare_write(cres, &subreq->start, &subreq->len,
@@ -218,7 +220,7 @@ static void netfs_rreq_do_write_to_cache(struct netfs_io_request *rreq)

atomic_inc(&rreq->nr_copy_ops);
netfs_stat(&netfs_n_rh_write);
- netfs_get_subrequest(subreq);
+ netfs_get_subrequest(subreq, netfs_sreq_trace_get_copy_to_cache);
trace_netfs_sreq(subreq, netfs_sreq_trace_write);
cres->ops->write(cres, subreq->start, &iter,
netfs_rreq_copy_terminated, subreq);
@@ -341,7 +343,7 @@ static void netfs_rreq_short_read(struct netfs_io_request *rreq,
netfs_stat(&netfs_n_rh_short_read);
trace_netfs_sreq(subreq, netfs_sreq_trace_resubmit_short);

- netfs_get_subrequest(subreq);
+ netfs_get_subrequest(subreq, netfs_sreq_trace_get_short_read);
atomic_inc(&rreq->nr_outstanding);
if (subreq->source == NETFS_READ_FROM_CACHE)
netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_CLEAR);
@@ -375,7 +377,7 @@ static bool netfs_rreq_perform_resubmissions(struct netfs_io_request *rreq)
subreq->error = 0;
netfs_stat(&netfs_n_rh_download_instead);
trace_netfs_sreq(subreq, netfs_sreq_trace_download_instead);
- netfs_get_subrequest(subreq);
+ netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
atomic_inc(&rreq->nr_outstanding);
netfs_read_from_server(rreq, subreq);
} else if (test_bit(NETFS_SREQ_SHORT_IO, &subreq->flags)) {
@@ -537,7 +539,7 @@ void netfs_subreq_terminated(struct netfs_io_subrequest *subreq,
else if (u == 1)
wake_up_var(&rreq->nr_outstanding);

- netfs_put_subrequest(subreq, was_async);
+ netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
return;

incomplete:
@@ -682,7 +684,7 @@ static bool netfs_rreq_submit_slice(struct netfs_io_request *rreq,

subreq_failed:
rreq->error = subreq->error;
- netfs_put_subrequest(subreq, false);
+ netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_failed);
return false;
}

@@ -1024,13 +1026,13 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
*/
ractl._nr_pages = folio_nr_pages(folio);
netfs_rreq_expand(rreq, &ractl);
+ netfs_get_request(rreq, netfs_rreq_trace_get_hold);

/* We hold the folio locks, so we can drop the references */
folio_get(folio);
while (readahead_folio(&ractl))
;

- netfs_get_request(rreq, netfs_rreq_trace_get_hold);
atomic_set(&rreq->nr_outstanding, 1);
do {
if (!netfs_rreq_submit_slice(rreq, &debug_index))
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index e5c049a25746..725b8fb8e4bb 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -18,6 +18,8 @@
#include <linux/fs.h>
#include <linux/pagemap.h>

+enum netfs_sreq_ref_trace;
+
/*
* Overload PG_private_2 to give us PG_fscache - this is used to indicate that
* a page is currently backed by a local disk cache
@@ -146,7 +148,7 @@ struct netfs_io_subrequest {
loff_t start; /* Where to start the I/O */
size_t len; /* Size of the I/O */
size_t transferred; /* Amount of data transferred */
- refcount_t usage;
+ refcount_t ref;
short error; /* 0 or error that occurred */
unsigned short debug_index; /* Index in list (for debugging output) */
enum netfs_io_source source; /* Where to read from/write to */
@@ -277,6 +279,10 @@ extern int netfs_write_begin(struct file *, struct address_space *,
void **);

extern void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
+extern void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
+ enum netfs_sreq_ref_trace what);
+extern void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
+ bool was_async, enum netfs_sreq_ref_trace what);
extern void netfs_stats_show(struct seq_file *);

/**
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 8c700e2bcd5c..507c5e612293 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -69,6 +69,17 @@
EM(netfs_rreq_trace_put_subreq, "PUT SUBREQ ") \
E_(netfs_rreq_trace_new, "NEW ")

+#define netfs_sreq_ref_traces \
+ EM(netfs_sreq_trace_get_copy_to_cache, "GET COPY2C ") \
+ EM(netfs_sreq_trace_get_resubmit, "GET RESUBMIT") \
+ EM(netfs_sreq_trace_get_short_read, "GET SHORTRD") \
+ EM(netfs_sreq_trace_new, "NEW ") \
+ EM(netfs_sreq_trace_put_clear, "PUT CLEAR ") \
+ EM(netfs_sreq_trace_put_failed, "PUT FAILED ") \
+ EM(netfs_sreq_trace_put_merged, "PUT MERGED ") \
+ EM(netfs_sreq_trace_put_no_copy, "PUT NO COPY") \
+ E_(netfs_sreq_trace_put_terminated, "PUT TERM ")
+
#ifndef __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY
#define __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY

@@ -82,6 +93,7 @@ enum netfs_rreq_trace { netfs_rreq_traces } __mode(byte);
enum netfs_sreq_trace { netfs_sreq_traces } __mode(byte);
enum netfs_failure { netfs_failures } __mode(byte);
enum netfs_rreq_ref_trace { netfs_rreq_ref_traces } __mode(byte);
+enum netfs_sreq_ref_trace { netfs_sreq_ref_traces } __mode(byte);

#endif

@@ -100,6 +112,7 @@ netfs_sreq_sources;
netfs_sreq_traces;
netfs_failures;
netfs_rreq_ref_traces;
+netfs_sreq_ref_traces;

/*
* Now redefine the EM() and E_() macros to map the enums to the strings that
@@ -273,6 +286,33 @@ TRACE_EVENT(netfs_rreq_ref,
__entry->ref)
);

+TRACE_EVENT(netfs_sreq_ref,
+ TP_PROTO(unsigned int rreq_debug_id, unsigned int subreq_debug_index,
+ int ref, enum netfs_sreq_ref_trace what),
+
+ TP_ARGS(rreq_debug_id, subreq_debug_index, ref, what),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, rreq )
+ __field(unsigned int, subreq )
+ __field(int, ref )
+ __field(enum netfs_sreq_ref_trace, what )
+ ),
+
+ TP_fast_assign(
+ __entry->rreq = rreq_debug_id;
+ __entry->subreq = subreq_debug_index;
+ __entry->ref = ref;
+ __entry->what = what;
+ ),
+
+ TP_printk("W=%08x[%x] %s r=%u",
+ __entry->rreq,
+ __entry->subreq,
+ __print_symbolic(__entry->what, netfs_sreq_ref_traces),
+ __entry->ref)
+ );
+
#endif /* _TRACE_NETFS_H */

/* This part must be outside protection */

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