On Mon 26-10-20 16:44:18, Waiman Long wrote:
> 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. 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 should have a size of 80 bytes. That
> means a system with 8GB or more memory will have the maximum value of
> 1048576 for inotify.max_user_watches. This default should be big enough
> for most of the use cases.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
So I agree that 8192 watches seem to be a bit low today but what you
propose seems to be way too much to me. OTOH I agree that having to tune
this manually kind of sucks so I'm for auto-tuning of the default. If the
computation takes into account the fact that a watch pins an inode as Amir
properly notes (that's the main reason why the number of watches is
limited), I think limiting to 1% of pinned memory should be bearable. The
amount of space pinned by an inode is impossible to estimate exactly
(differs for different filesystems) but about 1k for one inode is a sound
estimate IMO.
Honza
> ---
> fs/notify/inotify/inotify_user.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> index 186722ba3894..2da8b7a84b12 100644
> --- a/fs/notify/inotify/inotify_user.c
> +++ b/fs/notify/inotify/inotify_user.c
> @@ -801,6 +801,18 @@ 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) /
> + sizeof(struct inotify_inode_mark);
> + 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 +839,7 @@ 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
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
