The default value of inotify.max_user_watches sysctl parameter was set
to 8192 since the introduction of the inotify feature in 2005 by
commit 0eeca28300df ("[PATCH] inotify"). Today this value is just too
small for many modern usage. As a result, users have to explicitly set
it to a larger value to make it work.
After some searching around the web, these are the
inotify.max_user_watches values used by some projects:
- vscode: 524288
- dropbox support: 100000
- users on stackexchange: 12228
- lsyncd user: 2000000
- code42 support: 1048576
- monodevelop: 16384
- tectonic: 524288
- openshift origin: 65536
Each watch point adds an inotify_inode_mark structure to an inode to
be watched. It also pins the watched inode as well as an inotify fdinfo
procfs file.
Modeled after the epoll.max_user_watches behavior to adjust the default
value according to the amount of addressable memory available, make
inotify.max_user_watches behave in a similar way to make it use no more
than 1% of addressable memory within the range [8192, 1048576].
For 64-bit archs, inotify_inode_mark plus 2 inode have a size close
to 2 kbytes. That means a system with 196GB or more memory should have
the maximum value of 1048576 for inotify.max_user_watches. This default
should be big enough for most use cases.
With my x86-64 config, the size of xfs_inode, proc_inode and
inotify_inode_mark is 1680 bytes. The estimated INOTIFY_WATCH_COST is
1760 bytes.
[v2: increase inotify watch cost as suggested by Amir and Honza]
Signed-off-by: Waiman Long <long...@redhat.com>
---
fs/notify/inotify/inotify_user.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 186722ba3894..37d9f09c226f 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -37,6 +37,16 @@
#include <asm/ioctls.h>
+/*
+ * An inotify watch requires allocating an inotify_inode_mark structure as
+ * well as pinning the watched inode and adding inotify fdinfo procfs file.
+ * The increase in size of a filesystem inode versus a VFS inode varies
+ * depending on the filesystem. An extra 512 bytes is added as rough
+ * estimate of the additional filesystem inode cost.
+ */
+#define INOTIFY_WATCH_COST (sizeof(struct inotify_inode_mark) + \
+ 2 * sizeof(struct inode) + 512)
+
/* configurable via /proc/sys/fs/inotify/ */
static int inotify_max_queued_events __read_mostly;
@@ -801,6 +811,18 @@ SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd)
*/
static int __init inotify_user_setup(void)
{
+ unsigned int watches_max;
+ struct sysinfo si;
+
+ si_meminfo(&si);
+ /*
+ * Allow up to 1% of addressible memory to be allocated for inotify
+ * watches (per user) limited to the range [8192, 1048576].
+ */
+ watches_max = (((si.totalram - si.totalhigh) / 100) << PAGE_SHIFT) /
+ INOTIFY_WATCH_COST;
+ watches_max = min(1048576U, max(watches_max, 8192U));
+
BUILD_BUG_ON(IN_ACCESS != FS_ACCESS);
BUILD_BUG_ON(IN_MODIFY != FS_MODIFY);
BUILD_BUG_ON(IN_ATTRIB != FS_ATTRIB);
@@ -827,7 +849,7 @@ static int __init inotify_user_setup(void)
inotify_max_queued_events = 16384;
init_user_ns.ucount_max[UCOUNT_INOTIFY_INSTANCES] = 128;
- init_user_ns.ucount_max[UCOUNT_INOTIFY_WATCHES] = 8192;
+ init_user_ns.ucount_max[UCOUNT_INOTIFY_WATCHES] = watches_max;
return 0;
}
--
2.18.1
