Commit 92890123 authored Nov 08, 2020 by Waiman Long Committed by Jan Kara Nov 09, 2020

inotify: Increase default inotify.max_user_watches limit to 1048576

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 0eeca283 ("[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.

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].

We estimate the amount of memory used by inotify mark to size of
inotify_inode_mark plus two times the size of struct inode (we double
the inode size to cover the additional filesystem private inode part).
That means that a 64-bit system with 128GB or more memory will likely
have the maximum value of 1048576 for inotify.max_user_watches. This
default should be big enough for most use cases.

Link: https://lore.kernel.org/r/20201109035931.4740-1-longman@redhat.com


Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>

parent 7372e79c

fs/notify/inotify/inotify_user.c

+22 −1

Original line number	Diff line number	Diff line
		@@ -37,6 +37,15 @@

		#include <asm/ioctls.h>

		/*
		* An inotify watch requires allocating an inotify_inode_mark structure as
		* well as pinning the watched inode. Doubling the size of a VFS inode
		* should be more than enough to cover the additional filesystem inode
		* size increase.
		*/
		#define INOTIFY_WATCH_COST (sizeof(struct inotify_inode_mark) + \
		2 * sizeof(struct inode))

		/* configurable via /proc/sys/fs/inotify/ */
		static int inotify_max_queued_events __read_mostly;

		@@ -801,6 +810,18 @@ out:
		*/
		static int __init inotify_user_setup(void)
		{
		unsigned long watches_max;
		struct sysinfo si;

		si_meminfo(&si);
		/*
		* Allow up to 1% of addressable 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 = clamp(watches_max, 8192UL, 1048576UL);

		BUILD_BUG_ON(IN_ACCESS != FS_ACCESS);
		BUILD_BUG_ON(IN_MODIFY != FS_MODIFY);
		BUILD_BUG_ON(IN_ATTRIB != FS_ATTRIB);
		@@ -827,7 +848,7 @@ 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;
		}

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