Re: [PATCH] inotify: Increase default inotify.max_user_watches limit to 1048576

[Waiman Long]

On 10/27/20 12:00 PM, Jan Kara wrote:
> 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

I will certainly do that. Will send out a v2 soon.

Cheers,
Longman