netfs: Gather stats

Gather statistics from the netfs interface that can be exported through a
seqfile.  This is intended to be called by a later patch when viewing
/proc/fs/fscache/stats.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/161118139247.1232039.10556850937548511068.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161034669.2537118.2761232524997091480.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340397101.1303470.17581910581108378458.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539539959.286939.6794352576462965914.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653797700.2770958.5801990354413178228.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789079281.6155.17141344853277186500.stgit@warthog.procyon.org.uk/ # v6

fs/netfs/Kconfig

@@ -6,3 +6,18 @@ config NETFS_SUPPORT
 	  This option enables support for network filesystems, including
 	  helpers for high-level buffered I/O, abstracting out read
 	  segmentation, local caching and transparent huge page support.
+
+config NETFS_STATS
+	bool "Gather statistical information on local caching"
+	depends on NETFS_SUPPORT && PROC_FS
+	help
+	  This option causes statistical information to be gathered on local
+	  caching and exported through file:
+
+		/proc/fs/fscache/stats
+
+	  The gathering of statistics adds a certain amount of overhead to
+	  execution as there are a quite a few stats gathered, and on a
+	  multi-CPU system these may be on cachelines that keep bouncing
+	  between CPUs.  On the other hand, the stats are very useful for
+	  debugging purposes.  Saying 'Y' here is recommended.

fs/netfs/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-netfs-y := \
-	read_helper.o
+netfs-y := read_helper.o stats.o
 
 obj-$(CONFIG_NETFS_SUPPORT) := netfs.o

fs/netfs/internal.h

@@ -16,8 +16,42 @@
  */
 extern unsigned int netfs_debug;
 
+/*
+ * stats.c
+ */
+#ifdef CONFIG_NETFS_STATS
+extern atomic_t netfs_n_rh_readahead;
+extern atomic_t netfs_n_rh_readpage;
+extern atomic_t netfs_n_rh_rreq;
+extern atomic_t netfs_n_rh_sreq;
+extern atomic_t netfs_n_rh_download;
+extern atomic_t netfs_n_rh_download_done;
+extern atomic_t netfs_n_rh_download_failed;
+extern atomic_t netfs_n_rh_download_instead;
+extern atomic_t netfs_n_rh_read;
+extern atomic_t netfs_n_rh_read_done;
+extern atomic_t netfs_n_rh_read_failed;
+extern atomic_t netfs_n_rh_zero;
+extern atomic_t netfs_n_rh_short_read;
+extern atomic_t netfs_n_rh_write;
+extern atomic_t netfs_n_rh_write_done;
+extern atomic_t netfs_n_rh_write_failed;
+
+
+static inline void netfs_stat(atomic_t *stat)
+{
+	atomic_inc(stat);
+}
+
+static inline void netfs_stat_d(atomic_t *stat)
+{
+	atomic_dec(stat);
+}
+
+#else
 #define netfs_stat(x) do {} while(0)
 #define netfs_stat_d(x) do {} while(0)
+#endif
 
 /*****************************************************************************/
 /*

fs/netfs/read_helper.c

@@ -56,6 +56,7 @@ static struct netfs_read_request *netfs_alloc_read_request(
 		refcount_set(&rreq->usage, 1);
 		__set_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
 		ops->init_rreq(rreq, file);
+		netfs_stat(&netfs_n_rh_rreq);
 	}
 
 	return rreq;
@@ -88,6 +89,7 @@ static void netfs_free_read_request(struct work_struct *work)
 		rreq->netfs_ops->cleanup(rreq->mapping, rreq->netfs_priv);
 	trace_netfs_rreq(rreq, netfs_rreq_trace_free);
 	kfree(rreq);
+	netfs_stat_d(&netfs_n_rh_rreq);
 }
 
 static void netfs_put_read_request(struct netfs_read_request *rreq, bool was_async)
@@ -117,6 +119,7 @@ static struct netfs_read_subrequest *netfs_alloc_subrequest(
 		refcount_set(&subreq->usage, 2);
 		subreq->rreq = rreq;
 		netfs_get_read_request(rreq);
+		netfs_stat(&netfs_n_rh_sreq);
 	}
 
 	return subreq;
@@ -134,6 +137,7 @@ static void __netfs_put_subrequest(struct netfs_read_subrequest *subreq,
 
 	trace_netfs_sreq(subreq, netfs_sreq_trace_free);
 	kfree(subreq);
+	netfs_stat_d(&netfs_n_rh_sreq);
 	netfs_put_read_request(rreq, was_async);
 }
 
@@ -156,6 +160,7 @@ static void netfs_clear_unread(struct netfs_read_subrequest *subreq)
 static void netfs_fill_with_zeroes(struct netfs_read_request *rreq,
 				   struct netfs_read_subrequest *subreq)
 {
+	netfs_stat(&netfs_n_rh_zero);
 	__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
 	netfs_subreq_terminated(subreq, 0, false);
 }
@@ -179,6 +184,7 @@ static void netfs_fill_with_zeroes(struct netfs_read_request *rreq,
 static void netfs_read_from_server(struct netfs_read_request *rreq,
 				   struct netfs_read_subrequest *subreq)
 {
+	netfs_stat(&netfs_n_rh_download);
 	rreq->netfs_ops->issue_op(subreq);
 }
 
@@ -288,6 +294,7 @@ static void netfs_rreq_short_read(struct netfs_read_request *rreq,
 	__clear_bit(NETFS_SREQ_SHORT_READ, &subreq->flags);
 	__set_bit(NETFS_SREQ_SEEK_DATA_READ, &subreq->flags);
 
+	netfs_stat(&netfs_n_rh_short_read);
 	trace_netfs_sreq(subreq, netfs_sreq_trace_resubmit_short);
 
 	netfs_get_read_subrequest(subreq);
@@ -319,6 +326,7 @@ static bool netfs_rreq_perform_resubmissions(struct netfs_read_request *rreq)
 				break;
 			subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
 			subreq->error = 0;
+			netfs_stat(&netfs_n_rh_download_instead);
 			trace_netfs_sreq(subreq, netfs_sreq_trace_download_instead);
 			netfs_get_read_subrequest(subreq);
 			atomic_inc(&rreq->nr_rd_ops);
@@ -414,6 +422,17 @@ void netfs_subreq_terminated(struct netfs_read_subrequest *subreq,
 	       subreq->debug_index, subreq->start, subreq->flags,
 	       transferred_or_error);
 
+	switch (subreq->source) {
+	case NETFS_READ_FROM_CACHE:
+		netfs_stat(&netfs_n_rh_read_done);
+		break;
+	case NETFS_DOWNLOAD_FROM_SERVER:
+		netfs_stat(&netfs_n_rh_download_done);
+		break;
+	default:
+		break;
+	}
+
 	if (IS_ERR_VALUE(transferred_or_error)) {
 		subreq->error = transferred_or_error;
 		goto failed;
@@ -470,8 +489,10 @@ void netfs_subreq_terminated(struct netfs_read_subrequest *subreq,
 
 failed:
 	if (subreq->source == NETFS_READ_FROM_CACHE) {
+		netfs_stat(&netfs_n_rh_read_failed);
 		set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
 	} else {
+		netfs_stat(&netfs_n_rh_download_failed);
 		set_bit(NETFS_RREQ_FAILED, &rreq->flags);
 		rreq->error = subreq->error;
 	}
@@ -653,6 +674,7 @@ void netfs_readahead(struct readahead_control *ractl,
 	rreq->start	= readahead_pos(ractl);
 	rreq->len	= readahead_length(ractl);
 
+	netfs_stat(&netfs_n_rh_readahead);
 	trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
 			 netfs_read_trace_readahead);
 
@@ -722,6 +744,7 @@ int netfs_readpage(struct file *file,
 	rreq->start	= page_index(page) * PAGE_SIZE;
 	rreq->len	= thp_size(page);
 
+	netfs_stat(&netfs_n_rh_readpage);
 	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
 
 	netfs_get_read_request(rreq);

fs/netfs/stats.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Netfs support statistics
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/seq_file.h>
+#include <linux/netfs.h>
+#include "internal.h"
+
+atomic_t netfs_n_rh_readahead;
+atomic_t netfs_n_rh_readpage;
+atomic_t netfs_n_rh_rreq;
+atomic_t netfs_n_rh_sreq;
+atomic_t netfs_n_rh_download;
+atomic_t netfs_n_rh_download_done;
+atomic_t netfs_n_rh_download_failed;
+atomic_t netfs_n_rh_download_instead;
+atomic_t netfs_n_rh_read;
+atomic_t netfs_n_rh_read_done;
+atomic_t netfs_n_rh_read_failed;
+atomic_t netfs_n_rh_zero;
+atomic_t netfs_n_rh_short_read;
+atomic_t netfs_n_rh_write;
+atomic_t netfs_n_rh_write_done;
+atomic_t netfs_n_rh_write_failed;
+
+void netfs_stats_show(struct seq_file *m)
+{
+	seq_printf(m, "RdHelp : RA=%u RP=%u rr=%u sr=%u\n",
+		   atomic_read(&netfs_n_rh_readahead),
+		   atomic_read(&netfs_n_rh_readpage),
+		   atomic_read(&netfs_n_rh_rreq),
+		   atomic_read(&netfs_n_rh_sreq));
+	seq_printf(m, "RdHelp : ZR=%u sh=%u\n",
+		   atomic_read(&netfs_n_rh_zero),
+		   atomic_read(&netfs_n_rh_short_read));
+	seq_printf(m, "RdHelp : DL=%u ds=%u df=%u di=%u\n",
+		   atomic_read(&netfs_n_rh_download),
+		   atomic_read(&netfs_n_rh_download_done),
+		   atomic_read(&netfs_n_rh_download_failed),
+		   atomic_read(&netfs_n_rh_download_instead));
+	seq_printf(m, "RdHelp : RD=%u rs=%u rf=%u\n",
+		   atomic_read(&netfs_n_rh_read),
+		   atomic_read(&netfs_n_rh_read_done),
+		   atomic_read(&netfs_n_rh_read_failed));
+	seq_printf(m, "RdHelp : WR=%u ws=%u wf=%u\n",
+		   atomic_read(&netfs_n_rh_write),
+		   atomic_read(&netfs_n_rh_write_done),
+		   atomic_read(&netfs_n_rh_write_failed));
+}
+EXPORT_SYMBOL(netfs_stats_show);

include/linux/netfs.h

@@ -166,5 +166,6 @@ extern int netfs_readpage(struct file *,
 			  void *);
 
 extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t, bool);
+extern void netfs_stats_show(struct seq_file *);
 
 #endif /* _LINUX_NETFS_H */