From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Andrew Morton <akpm@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-kernel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH] proc/sysctl: drop unregistered stale dentries as soon as possible
Date: Wed, 08 Feb 2017 13:48:24 +0300 [thread overview]
Message-ID: <148655090380.421415.14305642138058304882.stgit@buzz> (raw)
Currently unregistering sysctl does not prune its dentries.
Stale sysctl dentries could slowdown sysctl operations significantly.
For example, command:
# for i in {1..100000} ; do unshare -n -- sysctl -a &> /dev/null ; done
creates a millions of stale denties around sysctls of loopback interface:
# sysctl fs.dentry-state
fs.dentry-state = 25812579 24724135 45 0 0 0
All of them have matching names thus lookup have to scan though whole
hash chain and call d_compare (proc_sys_compare) which checks them
under system-wide spinlock (sysctl_lock).
# time sysctl -a > /dev/null
real 1m12.806s
user 0m0.016s
sys 1m12.400s
Currently only memory reclaimer could remove this garbage.
But without significant memory pressure this never happens.
This patch detects stale dentry in proc_sys_compare and pretends that
it has matching name - revalidation will kill it and lookup restarts.
As a result each stale dentry will be seen only once and will not
contaminate hash endlessly.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
fs/proc/proc_sysctl.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index d4e37acd4821..1af7230c2c9e 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -852,11 +852,19 @@ static int proc_sys_compare(const struct dentry *dentry,
inode = d_inode_rcu(dentry);
if (!inode)
return 1;
+
+ /*
+ * Stale dentry: we cannot invalidate it right here, instead we
+ * pretend that it matches and revalidation will kill it later.
+ */
+ head = rcu_dereference(PROC_I(inode)->sysctl);
+ if (head && head->unregistering)
+ return 0;
+
if (name->len != len)
return 1;
if (memcmp(name->name, str, len))
return 1;
- head = rcu_dereference(PROC_I(inode)->sysctl);
return !head || !sysctl_is_seen(head);
}
next reply other threads:[~2017-02-08 10:50 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-08 10:48 Konstantin Khlebnikov [this message]
2017-02-08 21:48 ` [PATCH] proc/sysctl: drop unregistered stale dentries as soon as possible Andrew Morton
2017-02-09 3:53 ` Al Viro
2017-02-09 7:36 ` Konstantin Khlebnikov
2017-02-09 8:40 ` Al Viro
2017-02-10 7:35 ` [PATCH] proc/sysctl: prune stale dentries during unregistering Konstantin Khlebnikov
2017-02-10 7:47 ` Al Viro
2017-02-10 7:54 ` Konstantin Khlebnikov
2017-02-13 9:54 ` Eric W. Biederman
2017-02-18 18:55 ` Konstantin Khlebnikov
2017-02-19 8:42 ` Al Viro
2017-02-21 1:41 ` [REVIEW][PATCH] proc/sysctl: Don't grab i_lock under sysctl_lock Eric W. Biederman
2017-02-21 8:40 ` Konstantin Khlebnikov
2017-02-21 19:29 ` Eric W. Biederman
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