linux-kernel - [PATCH v2 04/25] netfs: Record contention stats for writeback lock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240814203850.2240469-5-dhowells@redhat.com>
Date: Wed, 14 Aug 2024 21:38:24 +0100
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <christian@...uner.io>,
	Steve French <smfrench@...il.com>,
	Matthew Wilcox <willy@...radead.org>
Cc: David Howells <dhowells@...hat.com>,
	Jeff Layton <jlayton@...nel.org>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Marc Dionne <marc.dionne@...istor.com>,
	Paulo Alcantara <pc@...guebit.com>,
	Shyam Prasad N <sprasad@...rosoft.com>,
	Tom Talpey <tom@...pey.com>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Ilya Dryomov <idryomov@...il.com>,
	netfs@...ts.linux.dev,
	linux-afs@...ts.infradead.org,
	linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	ceph-devel@...r.kernel.org,
	v9fs@...ts.linux.dev,
	linux-erofs@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Steve French <sfrench@...ba.org>
Subject: [PATCH v2 04/25] netfs: Record contention stats for writeback lock

Record statistics for contention upon the writeback serialisation lock that
prevents racing writeback calls from causing each other to interleave their
writebacks.  These can be viewed in /proc/fs/netfs/stats on the WbLock line,
with skip=N indicating the number of non-SYNC writebacks skipped and wait=N
indicating the number of SYNC writebacks that waited.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Jeff Layton <jlayton@...nel.org>
cc: Steve French <sfrench@...ba.org>
cc: netfs@...ts.linux.dev
cc: linux-fsdevel@...r.kernel.org
---
 fs/netfs/internal.h    |  2 ++
 fs/netfs/stats.c       |  5 +++++
 fs/netfs/write_issue.c | 10 +++++++---
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 7773f3d855a9..9e6e0e59d7e4 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -117,6 +117,8 @@ extern atomic_t netfs_n_wh_upload_failed;
 extern atomic_t netfs_n_wh_write;
 extern atomic_t netfs_n_wh_write_done;
 extern atomic_t netfs_n_wh_write_failed;
+extern atomic_t netfs_n_wb_lock_skip;
+extern atomic_t netfs_n_wb_lock_wait;
 
 int netfs_stats_show(struct seq_file *m, void *v);
 
diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index 95ed2d2623a8..5fe1c396e24f 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -39,6 +39,8 @@ atomic_t netfs_n_wh_upload_failed;
 atomic_t netfs_n_wh_write;
 atomic_t netfs_n_wh_write_done;
 atomic_t netfs_n_wh_write_failed;
+atomic_t netfs_n_wb_lock_skip;
+atomic_t netfs_n_wb_lock_wait;
 
 int netfs_stats_show(struct seq_file *m, void *v)
 {
@@ -78,6 +80,9 @@ int netfs_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&netfs_n_rh_rreq),
 		   atomic_read(&netfs_n_rh_sreq),
 		   atomic_read(&netfs_n_wh_wstream_conflict));
+	seq_printf(m, "WbLock : skip=%u wait=%u\n",
+		   atomic_read(&netfs_n_wb_lock_skip),
+		   atomic_read(&netfs_n_wb_lock_wait));
 	return fscache_stats_show(m);
 }
 EXPORT_SYMBOL(netfs_stats_show);
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 3f7e37e50c7d..44f35a0faaca 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -505,10 +505,14 @@ int netfs_writepages(struct address_space *mapping,
 	struct folio *folio;
 	int error = 0;
 
-	if (wbc->sync_mode == WB_SYNC_ALL)
+	if (!mutex_trylock(&ictx->wb_lock)) {
+		if (wbc->sync_mode == WB_SYNC_NONE) {
+			netfs_stat(&netfs_n_wb_lock_skip);
+			return 0;
+		}
+		netfs_stat(&netfs_n_wb_lock_wait);
 		mutex_lock(&ictx->wb_lock);
-	else if (!mutex_trylock(&ictx->wb_lock))
-		return 0;
+	}
 
 	/* Need the first folio to be able to set up the op. */
 	folio = writeback_iter(mapping, wbc, NULL, &error);